overdrive

Yes you can fit a Fairy O/D to the 4sp, but very hard to get.

I know where there is one to suit a 82 HJ47, not long rebuilt. It was swapped for a 5sp.

Marks Adapters make a overdrive for the cruiser, not sure if they are still avail. The 4 speed box with the overdrive is a stronger setup than the 5 speed.

One way to get higher gearing is to fit bigger diameter tyres or wheels. Even with engineering cert this may be cheaper than O/D unit or new box. Going from 30 inch to 33 inch tyres would give a 10% higher final drive ratio.

My brother in law has one on his 4sp trayback, I think it's made by Superwinch. It can split all gears by adding 25% if memory serves. i think it may have come from Marks adaptors but not sure.

well 55 if you can let me know about where this o/d is and how i can get in touch with em that'd be great