Best gearbox for a strong 186?

My M-20's have taken heaps , and have never blown one , worked 308 LC for five years ,injected 308 and hot sixes ,it depends what you want to spend , and how precise you want its application . it might be a hassle if one goes , but cheap and easy to replace ,the Holden diff is the weak point, and is what I had most problems with , some last no time at all , and others one will last years .
The diff ratio can be altered to help the Aussie box it meet your needs ,to a degree ,or use an M-21, it had designer ratios fitted for worked sixes , and was fitted to XU1's . I had one Supra box ,it was also good , with a 3.7 diff it was good an most areas , with fifth almost a highway ratio .