First, this is a question best asked over on the H.A.M.B. The people who post over there are way more familiar with this type of question than the people who post over here.
What (little) I know...
The Ford OHV are longer in dressed configuration (water pump, balancer) than the flathead Ford. This means cutting and recessing the firewall, or mounting the motor forward and using 6 cyl radiator, hood latch, and internal baffling. You will also requrie a modern radiator as the Ford OHV is designed for a pressurized cooling system.
Ford OHV have many configurations of exhaust manifolds and other accessories which do not always work on another block of the same "type". Sometimes it is "interesting" to get a Ford OHV to work with various steering systems.
Ford OHV typically have a front sump oil pan. This causes issues with clearance to the front crossmember. Summit Racing and Speedway sell rear sump pans with remote pickup.
Unless you can find an adapter to the stock transmission (and if you do you will break transmissions from too much horsepower) the Ford transmissions that mate to the OHV motor are not going to fit the stock center crossmember, surgery will be required. The brake pedal system will need to be new. The rear end will need to be replaced or converted to open drive line. The rear end installation will need to be modified to absorb the thrust (torque) of power being applied to rear tires. The rear brakes will need to be compatible with the front and new master cylinder.
There is more but thats what I can think of now.
A nice backyard project to start on Monday and get done on Saturday (several years later).
