On my Mk1 Vitesse have fitted relays and thicker wire and changed to halogen outers, dip a lot brighter but the wattage was higher, from memory 2 X 50 as against 2 X 37.5, never changed the inners.
I have fitted an alternator but that was due to a failed control box and quality, lack off, the ones on offer.
A C40L dynamo output at engine 1660rpm 25amp
A 15ACR alternator as fitted to later GT6 28amps at engine 2870rpm
Figures from workshop manual, can be affected by different size pulleys.
Regards
Paul.