How long did it take between their arrival and completion of testing/ driver training?
507001 was the first to be delivered on 29/09/78 and it entered public service on 01/11/78, although its first working with passengers aboard was the Royal Special (with 507002) on 25/10/78. Less than a month between delivery and carrying passengers with 250 miles of testing in between. Worth noting that 002 was delivered after 001 but was still able to be used on the Royal Special. Things take a great deal longer these days!
All the 508s were originally used on the Southern Region but the first units (508042 and 508043) left the Southern in 1981. Quite a number were used in service on Merseyside with their original numbers; I know 508003 and 508014 were two more.
People have the 508s down as the Wirral Line's replacement stock but the first arrivals from the South were in fact for the Northern Line and were not introduced to Wirral services for several years (summer 1984 IIRC). 508134 - 143 were originally based at Hall Road, not Birkenhead North, replacing a handful of Class 503s which had been temporarily cascaded from the Wirral Line for use on the Kirkby - Garston service.
Originally, 38 Class 507s had been ordered and this is reflected in the carriage numbering gaps (64400-04 are missing) and the order may have been scaled back because it was always anticipated that the 508s would transfer north to cover the shortfall.
Excellent photos by the way, The Sel.