"bigger cam = thinner shims. plus, you'll be adding new silencers which affect the measurements between the cam lobe and bucket. "

I don't know why this would be true. Perhaps if you were measuring gap at the top of the lobe...

And gap measurements should always be made without the silencers in place so they don't affect the measurement. Set the gap first, then put in the silencers.

Stock Volvo cams(and the VX was a stock cam in Euro market B230 engines)should have the same base circle. I've swapped cams a number of times from T's to A's to K's and have never had to re-shim. If you're dealing with a re-ground cam, you'll likely have to add shim thickness, not reduce it, since lift is gained by reducing the base circle dimension.

Cams from places such as Enem and KG Trimning who are grinding their own cams from blanks are the ones you need to be more diligent with. One "has" to assume that when Volvo grinds cams they keep the base circle consistent on each and every one.

Dale