8th Circuit: Republican 11.0 - 1.0 Democrat (the only total win in America -- liberals cannot win a three-judge panel here)
Conservatives are quite close to that point on the First Circuit. The last Republican-appointed judge on that circuit is assuming senior status soon (a GWB appointee). Two Republican appointees with senior status are no longer actively hearing cases. Assuming Biden gets a successor confirmed, that would leave zero Republican-appointed judges in active service and two in senior status (including the quite interesting Bruce Selya).Everything that you've said is technically correct, although it should be noted that Judge Gelpí was a W. appointee on the district court in PR &, for a Biden judge, is ruling well to the right of the mainstream, having just voted with Chief Judge Howard & the 'conservative' position in 2 immigration cases as well as in a recent 1A en-banc vote.
I think it's also worth noting that former Justice Souter also sits by designation on the First Circuit from time to time.
Unfortunately, Justice Souter hasn't sat-by-designation since Jan. 2020. Hopefully he'd like to return after the pandemic.
I imagine Justice Breyer would probably like to sit by designation on the circuit courts (or even district courts, as then-Justice Rehnquist did once while on the Court) from time to time, although I don't think there's anything in particular that would necessarily mean he would have to or want to sit on the First Circuit in particular.
Something tells me that the fact that Justice Breyer's home is <5 mi. from the First Circuit's main courthouse would probably make it an easier choice to sit-by-designation on than, say, the Fairbanks duty station on the district court in AK