I'd call and talk to Jerry or Jim at 22RE Performance.
Jerry's out this week, but guy on phone said he thought they could put a 20R kit together and to call back next Monday to confirm. He guessed cost would be about the same as the 22R ($160-180).
.....still trying to figure out what I want to do, probably no stop leak and just sell with it leaking and let next guy do what he wants. It's not like I'm selling because of the leak, I had listed it on CL a couple of days prior to discovering. I just noticed a tiny coolant drop under it where I park and investigated this. So I have a older write up somewhere about a mystery overheating issue at highway speeds (65+) held for long time periods (20 minutes or so). I had switched thermostats a few times, flushed system extensively, put in new radiator, and new water pump......all with no avail. The HG was kind of the last option without confirmation.....probably 40k miles later, it is confirmed.....I can't believe it held that long....I'll see if I can find that old post and note for other's reference going forward.