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.

the 400 and 390 are in the same family of motor (FE) 351m to a 460 will bolt in with using the same trans and mounts the only thing you have to watch out for is you rad size. if your goin from a 400m to a 390. there not to much of a difference, but the 400 has more grunt...If i where you i would be looking at a 460 if you want to go big.....go big or go home...it will cost a lil bit of $$$to get the 460 to a good 500or 600hp but will be worth it...

oooops sorry forgot to add watch out for what year the 390 is the small bolt bell housing has been around a lil longer that the big bolt....if its a small bolt ditch the 390 and go with the 351w there are more parts and you can make cheep hp with it....