I just got this via my father….

If PA, this would have been PA1 (PA’s RTW service), FRA 1530-LHR
1655/1800-IDL 2055

TWA701 also operated FRA-LHR-IDL (1500-1625/1730-2025)

Check-in at LHR in 1960 for international flights was indeed 60min prior.

We’re getting there!

Thanks for the input