bronco-79' 4x4 stock
4 speed
engine- factory 400
wonderin if i have to change engine mounts to fit 390 in my bronco?

i think you will need new mounts .( isn't the 400 a small block??)if you're swapping from small block to big block. you will need to change a bunch of things. radiator, manifolds,
possibly trans or bell housing etc.

what he said^ but i beleive id just stay with a small block, cheaper on gas, not much but some. plus u dont gotta do all that work lol,

400 motor uses same tranny bolt pattern as a 460, 390 has a round syle so it will ahve to be changed along with motor mounts.
Better route in my opinion swap for a 460.