I bought my TKO 600 from Fortes (
http://www.fortesparts.com/index.cfm). He modifies it with a Toploader input shaft so that you don't need a spacer or long bellhousing. I have an early frame with a 3.5" crossmember tube. The pad in front needs to be cut down and the holes relocated. I would have an interference with the tube if I used the stock TKO. You may also need to shorten your driveshaft with the stock TKO, I can give you measurements if you like. The transmission gear also gets changed to the T10 style. Otherwise the swap is pretty straight forward,
Art