Any reason not to run a 420 over a 465? I already have both, so that isn't a factor.
Pro's of the 420:
135ish vs 175ish pounds
shorter in length ~2 inches
smaller overall
reverse is near granny gear (down and left)
7.0 vs 6.55
Cons of the 420:
I'll have to machine an adapter to use a 465 bellhousing
Parts are more scarce and more costly (if needed)
I think the shift throw is longer
With either tranny I'm going to have to make an adapter for the rear and a new main shaft.