If you are going to use the stock mechanical fan, then allow 1" from the inside of the radiator core to the front of the fan blades for your "fore and aft" engine placement. Center the engine between the frame rails. The height of engine in relationship to the framerails always involves a bit of imagineering.----The higher the engine sets, then the higher the transission sets, so as a consequence you will end up cutting out a lot of floor and firewall to give clearance for the transmission and bell housing area on the engine, however you will have lots of room for your exhaust manifolds and steering shaft from the column to the steering box (which is always a real pig on a model A Ford).
You can set the engine lower in the frame, thus saving a lot of cutting and carving on the floor and firewall, but then you may have clearance issues with the exhaust and steering. This is really a "try it and see" type of thing----if you can find someone else running this set-up in a model A, then take some measurements from it. When all is said and done, a rule of thumb is that the lowest point on the oil-pan should not set lower than the lowest point on the I-beam axle. The engine should be set on an angle which lets the carburetor base set level (the engine will then be tilted down 3 to 5 degrees at the transmission end. You will have to fabricate engine and transmission mounts.