It does have the Roosamaster rotary pump.
Didn't have the problem before the overhaul but with the change in compression and new injectors could definitely see where this could be the problem now.
Did you rebuild the engine or was it done elsewhere? The change in compression isn't going to have anything to do with it.
If the probably actually began with the overhaul (and it's not just a coincidence), I can think of a few possibilities . . .
Somebody thought the engine smoked too much and turned the pump down.
Did anybody have that pump off during the rebuild??
Static injection pump timing is off a few degrees.
Rocker arms are way out of adjustment. If out of wack, they change quite a bit from a cold engine to a warm engine. And even if it was adjusted correctly at first, the new head gasket could of compressed a bit, and valve-lash would of gotten too tight. Usually after any rebuild, you're supposed to run the engine a big, retorque the cylinder head, and readjust the valves/rocker arms.
Also, if the pump is worn, and you put new injector nozzle tips in during the rebuild, they probably open now at a higher pressure. This slight increase of a few hundred PSI might be enough to cause a problem with a slightly worn, hot pump.