Hi Tintop, can recommend the Vitesse as a donor. Any Vitesse will do as they all sound awesome and really suit the 50's style race cars.
Early mk1's have a 70hp 1600, while the later mk1's ('67 on I think) have a 2 litre with 25bhp extra. Some time in '68 the mk2 was introduced with an uprated 105hp 2 litre and double-jointed rear suspension to replace the swing axles of the mk1. Don't fret over the swing axles on the earlier cars, the Sammio/Miglia/What have you cars are so light that there's no issues with jacking while cornering.
I'm aiming to go to Stoneleigh and I'll be driving this -
...as my next project still looks like this -
Hope you get to build your dream car - I did and I've no regrets whatsoever.