Im going to weigh in here again, just my opinion. I don’t think you will find a good powerhead for an engine of this age. By good powerhead I mean one with a good piston to cylinder fit that will idle well. As Don has pointed out the cylinder wall to piston fit is critical for this motor to operate well. Many a person (experienced mechanic as well) has a hard time diagnosising why those engines dye at idle when the cylinders are glazed or poor piston fit. I know y’all use your engines less in the north, cylinder wall glazing happens because of storing the engine and rust happening over & over and being scrubbed off by the rings. The cylinder walls look like the inside of a beer bottle. The symptom is a motor that dies away slowly at idle. You usually have to choke it to restart. The motor will run fine otherwise.if you look at your motor you will notice that there is no cross hatch left in the cylinders. Again like Don said, there are so many port in the middle of the jug most of the wear is in that area. It is hard to even measure because of the ports. A lite hone will show that the area is bigger. I just wish there was a way for you to get the powerhead here and back (shipping). Be happy to rebuild at minimum cost with over size pistons. But once again it would depend on as Don said what we would find inside. If crank and rods were good it can be done for less than you think. I hate to see you buy someone else’s powerhead with the same problems or worse. Those are great little engines. I like them much better than the 56 cu. in. beginning in 1986. The little motor was much better on fuel.

Dan in TN

Post some pictures of the engine, you just installed power trim/tilt, correct? Is the gearcase in good physical condition, no leaks/cracks/bent/broken skeg? Is it a fresh water engine? Like Dan says, a "used powerhead" will be just that, nothing like a freshly rebuilt powerhead to make that rig scream the way it should.
The other option to consider is just swapping the powerhead from the older non power trim engine to the newer blown engine with power trim. The only issue may be different shift linkage on the powerhead depending on the older engine’s year/vintage.