i was thinking the 5.3 myself but the aluminium block version L33 i think it is. lots of reasons to do it. mine is a Renix and doing this would rid me of so much Renix headache. do you have the weight differences of the 5.3 and the 4.0?
I have read varying specs on weight but from what I have gathered the 5.3 iron block/4L60E/231 combo is lighter than the 4.0/aw4/231. The aluminum block LS motors are about 80lbs lighter than the iron block so that would be even more weight savings.