The tuning calcs, both versions, are on the first post of my thead in the FM3 Tuning Marketplace.
This build reference is pretty basic.
A grip build would feature grip items of the next higher class, and power features of one lower.
The reverse would be true for a missile build. But any class has flexibility in numbers to at least one level higher and lower.
Differing tire widths can obviously throw some of the tire numbers way off,...I just average them out for reference.
There are too many variants of power-to-weight for this to be anything more than a rough quide too, but it gets you pointed in the right direction I think.
A muscle car, for example, kinda blows the actual power and weight values out of whack, but the power-to-weight ratio and grip levels will be within tolerances.
Another example is aero. My A-class Porsche GT2 has no aero but runs very well.
Its just a rough guide.