When I first converted my S3 to v8 I ended up without a spigot bush as all - the only result was an odd noise from time to time when depressing the clutch, however I looked at machining the crank end or making up a thin wall bush and when I dropped the engine out to replace the heads etc. I fitted a spigot bush adapter that meant cutting about 6mm off the crank end - to do this I simply dropped a bit of plate over the spigot and took it off the bit sticking out with the angle grinder. The gear change seems slightly smoother but its hard to tell.