I have some m18 drag links from when I was going to build a Haynes. In the tiger book it says to use a m20 version, is there any reason that I can't make new bushes with the m18 thread and use the links I have. Iv tried them in my cortina uprights and there the correct taper.

None at all, I use landrover TRE's for my uprights.

Regards Mark

Can't see an issue if your building the wishbones etc yourself.