[Keithc8]

It is not uncommon to run 38 to 40 degrees of total timing on these engines. The heat gun is of no use unless you have someone under the hood at wide open throttle measuring the temp about one inch down from the head. I assume you are taking a reading when the engine is at idle. The jets will not change this temp any since this is controlled by the idle circuit and air bleeds. You will have install thermo couplers about one inch down from the head and check at wide open throttle. The temp should be in the 1200 degree range to be on the safe side.
The other way to check this out and get the car tuned right would be to put on a chassi dyno and measure the air fuel ratio as well.
The other engine may have had richer idle circuits which would have showed lower temps at a idle. Good luck, Keith