For completeness, I thought I should post my results.
First, a million thanks for the recommendation of Scandia Prop & Hydraulic shop in Fairhaven, MA. Great folks, they always answered the phone, they had the rebuild turned around the day they received it, and the owner came in on his day off to give me the pump back on my way down to the boat. No doubt you can find great small shops like this in other places, but I can vouch for this one. The visit to New Bedford/Fairhaven was like a pilgrimage for this old fisherman, and just being in that shop, surrounded by hulking old machines and enormous props, was good for the soul. And he only charged me about $100, $30 of which was for the parts.
The install went well. I hooked up the center (smaller) line first, so I'd have plenty of room on either side to swing the wrench. Then attached the port and stb lines. For some reason, mine was installed upside down, with the hydraulic lines coming off the top. Because the lines were in a bundle with a bunch of wires, and the manual says it doesn't matter which way it's installed, I left it that way. That turned out to be a help later, but I noticed the line marked with red for "port" was on the starboard side, and vice-versa. No problem, once I realized it was upside down.
With the lines connected up top, I went down to the reservoir and put a little pressure to it (15 lbs or so). Went back up top. Couldn't see or hear any leaks. Cracked the connection on the port, then stb side, one at a time. Got a little air coming out. Closed them again.
Went down below again and pressurized to 55 lbs. Waited 10-15 minutes. No change in pressure. Back up to the helm. Cracked each line again, this time waiting for the air bubbles to stop and only fluid to leak out. Waited a minute or two more to be sure. Tightened the lines one last time.
Because the hydraulic lines connect at the top, bleeding this way should, in theory, have removed almost all the air. If it was hooked up right-side up, there are two hex nuts on the bottom (which would be the top) that I think are for bleeding. Anyway the break-out parts diagram shows them with gaskets, so I suspect that's what they're for.
Back below, I released the pressure, removed the fill cover and filled the reservoir 3/4 full (it had been down to 1/4). Pumped it back up to 55 lbs. It took exactly one quart (I had bought 3.)
Up at the helm, I turned it 5-1/2 turns to port until it stopped. Then 4-1/2 turns back to starboard to the stop. Then back and forth, each time only 4-1/2 turns stop-to-stop. I'm taking that as a good sign, since 4-1/2 seems about right, and it was consistent every time (after the first.)
12+ hours later, the pressure is still at 55 lbs. I'll back it down to 40-45 like the manual recommends later, for now I'm leaving it high to verify there's no pressure loss.
My "little" job for the day, replacing two courtesy lights, turned out to take far longer, and involve more parts & tools, than the helm pump replacement. But that's a story for another day.
