I have done the same swap in my "47 Mercury 1/2 ton (which is the same as the Ford). It's really not too hard but there's a few things you need to know:
1. The water pumps in the 8BA car will not work. You need to put in truck water pumps
2. If the bolt pattern for the "6" transmission is the same as the V8, you need a "49-'51 Merc bell housing. to get the two to match up
3. Rebuild the radiator if you have it and have the radiator guy put in smaller inlets and outlets to match the outlets of the 8BA. Note the car radiator will not fit into the truck radiator frame.
If you need a 3 speed truck V8 for the '42-'47, I have one that available. Private email / text if you would like more detail info. Good luck!