So 1974 under RFK = 1994 under WJB?
I would say 1970 would show slight GOP gains (depending on how 'Nam is going) and 1972 could see some noteworthy GOP pickups, because RFK would be fighting for his life, even against a weak nominee, thus the focus would be on the presidency, not congressional elections. Reagan plays it cool, and campaigns mainly for congressional GOPers, knowing his time is 76. 1974 could be about the size of OTL 74, but with Dems on the receiving end after 14 years of democratic dominance. I'd say between otl 66 and otl 74 size gains for GOP in TTL 74. 76 could bring GOP gains the size of otl 1980, at least in the house.