I would guess electrical or fuel.
Change condenser, points as well if youve got any.
fuel pressure next - check output from pump is healthy
check carb isnt blocked with crud (you will need to strip it to a degree to find out)
I've had a 600D I used to do production car trialling in - sadly no photos. They are rare in the UK, but look what I found in a barn in Menorcal last year - there were 3 of them