well if i was to do it id mostlikly end up makeing my own motor mounts and ect...both builds depending on the one i do are getting a 200 shot of nos and atleast a vortech threw a carb so if that makes a diff
I think a 429 would be easier than a 428, plus there's already kits to drop 460s in foxbodies, so all the work is done for you if you go that route (460 is just a stroked 429). Boss 429s can put out over 600hp with just a few mods (cam, carb, exhaust), I'm not sure what's special about the Boss motor, I'm assuming it's at least different heads.
That doesn't answer your question, though.
I think it depends on how you're gonna use the car. The big block is going to put at least another hundred pounds on your front end, so for a street car, I'd stick with the small block. I think the big block will make more power, though, and make it more reliably. I have NO data to back that up, so take it as you will.
Swap out the iron heads and intake for aluminum and you will be close in weight to the small block. Should not be enough difference in weight to have to change to stiffer springs and such in the front. I would go with the 351/427 stroker route, but I am partial to them also.