John,
You are quite correct. There is a big difference in a pure track car and a road car. (If you wish to make them both optimal that is.)
Your approach with 2 sets of everything would work well on the JBL as you would not have to make any other changes outside of camber and toe settings. (And the engine/gearbox/rear gear.
)
I think the 2.5 rack for road use would be OK but I have some concerns about 75 mph crusing comfort. The car really does not need much steering input at speed as you know.
First I would add in a bit more caster than the 3 degrees that I spec. More like 4.5>5 degrees and see how the low speed steering is before you change the rack.
The front wheel rates are a bit high for road use as well. Are you running the 175 springs or the 150's? With your rockers I think that 150 or even 125's might be the best rates.
I bet the spec racer is interesting to drive. Anytime that you have limited motor like that you really have to rethink how you drive. Momentum is very important as I am sure you have found out and really requires entirely different chassis think to work well.