Troubleshooting by remote description is hard to do, but here are some thoughts.

I'm assuming you have the L-134 flathead. The good thing about the flathead is that there's nothing to get in the way of a piston as it comes up - unless someone left a shop rag in the top of the cylinder (very unlikely...). Not much risk of breaking anything by cranking it.

A. Turns over slower than it should with plugs removed. A newly overhauled tight engine will turn over slower - I can't judge just how much slower it is, but that may or may not be a hint of what's going on.

B. Won't crank with plugs in. Sounds like there is a timing problem where you are trying to compress a cylinder full of air against a closed set of valves. The good news if this is the case is that you probably have good valve seating and solid compression. The bad news, you'll have to take some things apart to see what's happening. With the L-134 it's easy to pull the head and check how valves are opening as you come up to TDC.

You might try just putting one plug in. Crank it - and if it stalls against one plug, I'd suspect the valves aren't timed properly.

Or - as we have all found at one time or another with old Jeeps - it could be something totally different.

Let us know what you find. Someone else is having the same problem, they just are afraid to ask and we need to know.

And, oh by the way - if the dipstick gets up against a counter weight on the crank - it makes a real racket but doesn't hurt anything right away.....Gets your attention though!

Just discovered that today.....