Holinger are making a HZF, 5speed H pattern gearbox, in either dog arrangement or synchro.
Std ratios are 2.29 1st and 1:1 5th.
Dog leg.
Price is around $12g brand new.

That'll be what I'll do once my option box is no longer usable, it's getting harder and harder to justify the money that has to be spent on a 40 year old gearbox.

Cheers
David.