Another thing worth considering is the condition of the battery leads. I did a similar job years ago. Before I had the engine out the engine turned over pretty well, however with new rings, shells and seals it turned over to slowly.
A friend suggested that it could be the battery leads as he had experienced the same problem on an escort van. I admit I was dubious as the Jeep had thick 6V leads and I was running with 12V. I replaced them with new 12V cables and the engine flew over and fired up. When I stripped the old leads it was clear that they had deteriorated over the years building up a massive resistance, which only came to light with the tighter engine.
If you are running 6V the correct size cables can be made from 70mm welding cable and correct crimp lugs, incidentally it helps to fit an extra earth lead from the battery tray to the steady bracket at the back of the starter motor.
John