I've got a 1.6 driver and doing a brake upgrade, I believe the non gti's had 7" servos and gti's 9"
question is, are there 9" servos that will fit in any other model ie mk3?
I can't say for sure but I'd expect a base spec mk3 could be a donor. Alternatively Polo, SEAT Ibiza, Inca etc might be an option.
Could you used https://7zap.com/en/ to compare part numbers?