another overheating problem

225 slant six. Not the original motor that came with my 76 dart.drool tube head. Holley 1945 carb which I rebuilt but did not take to much attention adjusting the float and the get vacuum amplifier nipple fell out and the opening inside knocked down to block it ( might not have been the best thing).
So last year I think it was or just about I tore apart my head and replaced all the gaskets and rubber. I used a felpro kit.
I didn't realize it said no retorque on it and I retorqued it like the book said. It was leaking coolant down the block before I retired it is why I did when it reached operating temp. And the coolant stopped dripping
Well it started over heating more recently and tore the head back off. It was puking out the rez. After changing the cap and tstat a few times I took the water pump off and it seemed fine. Which is why the head came back off.
I put a level on it as it's the flattest thing I have ran a feelers by it and it's straight. I used a .381 feelers as the book says anything more needs resurfaced but by looking at it I think it's about perfectly flat and I don't thing my smallest feeler would get under it.
I don't have anything small enough to check the block in the car.
Could the block be warped? Maybe the initial coolant leak cause a pocket under the gasket allowing continued leaking.
I removed the head by myself with my cherry picker so the gasket wasn't in best shape to look at by the push rods but around the cylinders it looked fine. I'm not sure what could be the issue. I do know I did get an exhaust leak at the exhaust manifold/down pipe and it was blowing out toward the block.
I do want to replace the piston rings but I may have to pass on this still. I can handle a bit of blow by til I can make enough money in the next few months just to send it to the machine shop. I'm sure I can't remove the rings right now as the ring wear is probably gonna get in the way like my other block sitting under my awning. I maybe wrong and ring compressor might actually fit but risk. Haven't changed rings before. I might just take the whole block in and have it rebuilt professionally but I don't generally trust shops which is why I work on my own vehicles.
O and I did notice a bunch of gunk building up around a couple of th spark plugs so I'm sure something is wrong in the head. It drive all summer with a bad clutch til it went out and I replaced it. The over heating started about a month ago I think. Blew up my radiator which I learned how to sweat it back together just for it to blow on the exact opposite. So I'm hoping my radiator out of my 78 b100 slant six will work, if it's still good. It's bigger but I think it might work even if I have to drill some extra holes to mount it in.
Thought, ideas, and no I'm not putting a v8 in it lol