Around three valve sets there was heavy rust. I scrubed them with a wire brush and the block surface is rough and chips easily. Is this block any good? It doesn't have any cracks. How far can you deck it? Is there anyway to tell if you have a 4" crank other than the checking the stroke with a piston. What is the best way for removing stuck pistons?
Questions about Flatheads are better answered at the sites listed below. Some of these guys have better that 50 years workin these beasts.
Be nice and they will give ya all sorts of information.
Nathan, what's the history of this engine? Sitting outside, carb off, heads off, intake off, etc.?
Soak the stuck pistons with a good penetrating oil - Marvel Mystery oil, diesel fuel, PBlaster, etc. You'll also want to soak the valve train cause if the valves are that rusted the valve train can keep the crank from turning until you strip the fiber gear on the cam shaft (guess how I know that?)
If soaking doesn't loosen it up, start disassembly. Eventually get the crank out. Pistons that have rings that are really rusted to the bore can be broken up and removed in pieces. Anything that attaches to the block can be replaced - at cost of course
Easiest way to tell is to measure. If you have one piston that is up and flush with the top of the block, you should have one that is at the bottom of its travel.
The blocks don't deck well cause the water jacket is so close. The head bolts go into the water jacket, so decking will remove thread depth. Your machinist can tell you if you have a workable block. If there is rust in any cylinders, suspect a crack.
And Dick is right about those two groups - they're a super bunch of guys.
The truck sat outside for twenty years without a hood. So rain went down the oil bath filter through the carb and rusted the valves pretty good. I got all the pistons out. 1 by hand, 5 by wood block and two by 1" steel rod. Can you get valve seats for these engines? since that would solve my problem. I think I'll ask about a different engine just down road just if I need to get a different engine.