I hate to ask....but what's it worth?

Get it running if it's simple enough and see if it is internally water tight. A running engine allows you to make a good decision. Flatheads aren't cheap to build or common enough to find every day. Hesitation to use one is understandable. If it is good enough to put money into, and you're inclined to spend a bit to have that old engine work for you, it's hard to imagine that you would be sorry for using original Ford power.

 

Started messing around with it a little today. Put a battery in it and got nothing. Jumped the starter relay and get a slow crank/groan out of the starter a couple of times but nothing real great. The fan did rotate though. Pulled the starter out and I'm going to have that checked out. Probably should rebuild or clean up the carb.
Off topic here but I have drug home some real pieces of crap before so I've seen it all but I have NEVER seen so much rat shit in my entire life!! I have dumped my shop vac twice now....completely full. Finally, when we were vacuuming out the glovebox, found the culprit. Dead as hell but pulled out the crappin' bastard. Had a 7" tail on him.

 

rodents tend to like old trucks for some reason. Careful with the rat crap though as sometimes it carries stuff you don't want to catch.

There are about five questions that pop up on a regular basis that always get a guy, especially an fng a ration of crap and probably at the top of the list is the wiw
question just above the will a 350/350 fit question.

The value of a flathead like that depends on several things and probably number one is it's overall condition. Cracks/no cracks? Secondly is which flathead it is. Last is who's selling/who's buying and where it is at.
The "oldtimers" probably say to throw a 302 in it just because it would probably be less expensive in the end run and the truck will be able to run down the highway with the big dogs or lead the pack for hours on end where the flathead would make you inclined to cruise at a bit slower pace.
The cars I've had in my adult life have always been road burners that could eat up miles with abandon and now at 62 I have just bought the first flathead I have owned in 42 years just because I want one. It may not go down the freeway at 80 for hours on end like my 51 Merc when it had the 350 Olds or my 48 Pickup when it had the 350 Chev but I will have just as much or more fun with it.

 

Any motor can be reliable if maintained, and treated as it was meant to me, after all they ran good from the factory, some take a little more tinkering than others but that's just part of the fun

Enjoy it, good luck!