Yes and No!

Yes I know the answer and No it won't fit. A bellhousing from a sbc or bbc will fit on a 250. If placing a 250 in a pre 1954 truck, The rear engine crossmember will need some work. It may be possible to swap the original crossmember with one from a 54-55.1 truck. The later crossmember will line up with the "angled" bellhousings of the post 1954 trucks.