Pull it, that will make the job easier. Mark it where the base meets the block. Just stick a screwdriver down at the base where it touches the block and dist housing base and give it a whack. You have a permanent mark. Take off the top half of the cap and mark where your rotor is pointing. I used a knife, I dont want it rubbing off. Then pull the T-stat housing and put them back in reverse order. The t-stat housing can be a pain with the dist in place.
You have a good manual and fel-pro gasket set with rubber ends? You know where to put the small dabs of RTV in the corners where the block meets the head, right?