I did the swap on my 68 Mk1 this year - Pretty easy swap out although if you get a kit, the top bracket you get will be useless as was the fan belt supplied - just adjust the old top bracket and buy the right length belt - mine needed a 1500 mm one
Anyway - even though my dynamo was OK, my lights are brighter and I can now fit other electrical ancillaries if and when I want to without any concern