As I posted earlier you will get more for the engine if you can show that it runs.
Flatheads that do not run go for whatever you can get for them. Realistic prices for unproven ones start at $200-$300.May top out at $500 if someone falls in love with it. You will see them higher but I have also got them for less. If you can get it running then I would think around $650 and up.
Check some of the other sites on the internet for pricing. I check E-pay just to see what prices things aren't selling for.
2 big problems with the flathead. Many of them have cracked blocks. Some of which can be repired. Some not. First thing that has to be done is to pull the heads and visualy look for cracks. Also the cost of rebuilding has become expensive as well. It is not unheard of to spend $5000 on rebuilding even a stock one. But that price will depend on what you can do yourself. Plus not every shop can do a good job rebuilding as they have some peculiaritys.
As for the trans. Most of those big old heavy duty 4 spds go for scrap. They are geared so low as to make driving at anything above 50 MPH a real chore. You might get lucky and find a restorer that needs one.
The 8ba motor in your truck has a seperate bell housing from the block much like a newer type engine. My advice would be to switch over your entire drive line. Engine,trans and rear end if this is something that you plan on driving a lot
Hope this helps you out.
Torchie