Deployable/sometimes stowed inner forestay,

Here is how we did it on the old boat for some southern sailing.
It was a 42 foot 7/8 fractional rig boat
Firstly measure the height of the mainsail headboard with two reefs in.
Get a rigger to put a "t" ball fitting at that height
At an angle parallel to the forestay install your inner forestay tack off point and reinforce the underdeck and make a tie down to the hull if you don't have a bulkhead handy.
Move the topping lift exit to just below this height and increase size of topping lift (10mm dyneema in our case)
Then put two more "t" ball fitting a little below on the side of the mast section.
The rigger will give you "t balls" which are cut short and have ring welded to the ended.
Splice up an inner forestay out of 10-12 mm dyneema of stripspeed and bend on to the "t ball" ring
Do the same for the check stays which should terminate about 1m short of your spinnaker blocks.
Get a staysail with hanks made up to put on the inner forestay making sure you can sheet it on your existing tracks.
Make up some tails for check stays so you run them to your cabin top winches from your spinnaker blocks
The rest of the time the dyneema inner forsetay and check stays are just tied off or the "t balls" taken out when you are just weekend sailing or not ocean sailing.

So the drill is while you have two reefs in the mainsheet will hold up the middle of the mast against the inner forestay.
After that use the check stays to hold up the middle of the mast.
Leave the staysail hanked on until you have to furl the headsail completely.
Deploy when ready.
The difference it will make to the motion of the boat is amazing.
And if you do go upside down the rig will most likely stay in the boat.
I will try to find some pics

But a lot depends on the boat and you have to sail in plenty to learn what works.
There would not be much point doing this with a Currawong for instance but a Cav 37 is different again.
A late model IMS raceboat would charge upwind perfectly balanced with only a baby storm jib and nothing else in plenty because of the odd keel position and the efficiency of the keel. (until it stalled of course them you just blew sideways until the flow reattached)
As Shaggy is learning of late, "If you don't go you don't know!"

That's all very nice but the original question was for a Tophat. These are a very small yacht in todays terms and all that extra hardware whizzing about at the top of the mast is not going to help much. The fore deck is not that big either and I think simplicity is the answer. Good headsail furler and a well designed headsail about 110% is probably all it needs.

The comments of late seem to ignore the original purpose of this thread, which was about a Top Hat and nothing in the magnitude of the 37's and 42's.
The chap who started the thread is a learner and still grapling with basic sailing terminology. So do many others who are perhaps 50-60+ late starters, are cruisers not racers, who are playing with boats at leasure, not thinking of crossing oceans or winning the next race.
So, they do not need extra baby stays, inner fore stays and reinforcements to their yachts. Let alone made of Dynema! Struth!

The Tophats are not buit for ocean crossings and this fact should not be ignored before starting a passage. They are nice little boats with potential, a northern trip is a realistic plan, but it does not need a huge undertaking to fit expensive things which are not going to increase the sailability the safety nor the resale value of the boat.
One might protest of my last sentence, l see the brow's of many rising. I stand by my comment in the light of the following:

First, sailability is not going to be imoroved upon by fitting a furler. Perhaps the opposite is true. (a mast furling main nearly killed one, l remember, in the Bay of Biscay in a blow! )
Secondly, a furler is not safer than hanks (specially piston hanks!) if the sailor has thrown caution into the wind and does not seek shelter from the elements when the signs are obvious.
Thirdly, the yacht, old as it might be, is going to be the same old yacht like before, before it has been adorned with additions an old sailor might frown upon.

One would not say the same about a reliable built in engine or a life raft of some sort let alone a jack line, or a PFD with harness.

Couple of things, Top Hats as long as well built are definitely an ocean boat.
Last Australian to sail the Great Capes solo did it a Baker built Top Hat with an outboard motor on the back.

As to other questions!

A Compass 28 strikes me as a perfect boat for the inner forestay staysail as the boom is very long and rig is forward so with no headsail or furled headsail nothing will balance the reefed main where the rig is quite forward.

Also a Top Hat is similar in this respect but not as pronounced but still a good choice as it would mean all your sail area is down low as well.

The Currawong is different altogether because the rig in well forward of the centre of the keel but the mainsail is so very small when reefed so you don't get the huge balance problem.
I suspect that you would not have the inner forestay take off that far forward in the foredeck otherwise you would defeat the purpose of getting load out of the front of the boat.
So maybe I will revise what I said about a Currawong with that qualification.
I did own a Currawong for a short time years ago but never had to go into harms way.

However I am sure Alex used an inner forestay staysail on Berri all the time. So it would be interesting to ask him but the mainsail on a Brolga is much bigger than a Currawong in a relative sense.
Hope that helps.

Berri is very similar to MB. I took a lot from Alex's voyages.