we did a cheap, nasty, but brutally effective turbo conversion on an A14 a few years ago.

used an ACL head shim to help decompress a little. I think these are .030 or .040".

removed the mechanical advance mechanism from the dissy and ran it fixed at 10-12 degrees (but we only used LRP -lead replacement petro which is pretty low octane), and had a dodgy water injection system.

we left the bottom end standard and used an 8000rpm redline! Only problem we had was caused by a broken ring which more than likely happened in the first week when we were tinkering with what it was all about and trying to get the detonation under control. it eventually lead to a broken headland on #4 piston.

std clutch would slip at anything over 4lb boost. we used a heavy duty RPM clutch which was still borderline - you had to be gentle with your shifts, but that was probably a good thing for the standard gearbox and diff. RPM also make a sprung centred puck clutch, which is where I would start if I did it again.

We destroyed a tailshaft so I would caution on using a standard one. The mangled wreckage of it looked like exhaust pipe! Not exactly heavy duty...

that's all I can think of for now