Have an 85 F350 with a 351M I think. I know it is a 351 not totally sure about the M part. 6 bolts in valve covers if that helps. Would the bell housing from a NP435 that was attached to a 302 bolt up, or will it require a different bell housing? Will a newer version bell housing with a hydro clutch work? When going from a flex plate to a fly wheel, will I have to change the front balancer?

W, so the 302 bellhousing matches it

pic of 8 bolt M valvecover for reference

Have an 85 F350 with a 351M I think. I know it is a 351 not totally sure about the M part. 6 bolts in valve covers if that helps. Would the bell housing from a NP435 that was attached to a 302 bolt up, or will it require a different bell housing? Will a newer version bell housing with a hydro clutch work? When going from a flex plate to a fly wheel, will I have to change the front balancer?

Ford didnt offer a 351m after 81. If you have an 85 then it is a 351w. The windsor also has 6 bolts.

The bellhousings will swap from a 302. The flywheel will not because of differences in the balancing. You will have to use the 351w flywheel, but you wont have to change the front balancer.