I have a Spitfire with a 302 four speed setup, and have a GT6 waiting for either a 460 or Barra (I have both engines already). The problem is that the Spitfire is sitting mighty low right now. There must be something out there that uses a similar sized spring with a higher rate that can be fitted. There are spring manufacturers close by, but I am building on a budget of almost nothing and I repurpose anything I can whenever possible.
Also looking for a radiator that will fit better than the one I have, The previous owner of one of my cars used a smaller radiator (motorcycle?) on each side of the main one. I might try that again or use the trunk (boot), but don't really want to eliminate the luggage capacity.
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You might do better to ask such chassis-related questions on the Triumph Sports Six forum.
https://www.tssc.org.uk/tssc/index.asp
Be ready for some pushback, not everyone appreciates modified cars, but the fact that it wasn't your work may provide an excuse !!
Ivor