The 764's have a single international config which include both PS and C+ cabins. There is no domestic variant of the 764. When these aircraft are flown on domestic routes, they are selling and marketing the PS seats as C+ seats and fares, while the C+ seats are marketed as preferred seats. This is because there are simply no PS fare filings on domestic routes (they only exist on specific international routes). They are flying international aircraft more widely on domestic routes these days due to the slack in international flying due to Covid. Old domestic F 763's (which are no longer in fleet) were 6 across in F and seats were slightly narrower than PS seats (18.5 vs. 19 inches). However, I don't think that includes the armrests and the old domestic F aircraft had independent armrests for each seat rather than a shared one in the middle like PS -- http://web.archive.org/web/201702080...-300_D_New.php