I finally got the trim-tilt up and running. Next trip down it goes back on the boat. I ended up having to helicoil three of the four threaded holes in the gear pump housing due to drilling out broken bolts. Welding didn't work because there's just not much strength in a 1/4-20 ss cap screw. They just twisted off again.
During reassembly, I hit a snag. I had a small metal bit with a hole left over. It was a metering orifice by appearance. I hadn't mated the gear pump- motor back to the main assembly yet. There was nothing that matched this part either in the service manual or online. So I downloaded the pictures I took during disassembly, and there it was, in the bottom port of the main assembly. Back it went, finished reassembly, topped up the fluid, hooked up my test harness, and fired it up.
Worked great, no leaks, didn't even need much purging. Whew! Minus parts cost, saved about $2.5k on that deal. That's assuming a retiree's time is free, which is pretty much the case.