The 4 speed was not around when I did all this. If it was I think I would go that route VS the Klune-D20. But I wish they had the 4.3/2.7 4 speed.
The only way I could afford to do the whole thing was by buying what I could afford and gathering the parts little by little. With the 4 speed it's a pretty big pill to swallow all at once, plus D-shafts.
Both the D300 and D20 are nice cases. Their biggest weak link is the output shaft strength, but with the motors we run I don't think it's a problem. Most of the stories I have heard is the V8 crowd with leadfoot driving styles. I don't miss the chain.
My buddy with the Klune-231 has not had any trouble with his. I don't think he is running the wide chain. But his is a trailer queen, with not alot of street miles. That is still not a bad option either.