I was almost correct...Its close to being the same as a Mauser 98..real close, but just enough difference to cause all sorts of scope alignment problems. These are problems that wouldn't arise with the Redfield mounts because they can compensate for slight errors in alignment. So the Redfield mount for a Heym SR20 will fit a Mauser 98.

Anyway, I finally figured it out...good thing I have a lot of various Weaver and Weaver-type alloy and steel bases....it was an endless mix and match and I finally got it sorted, but it took time...For the front base I used a steel Warne Maxima Weaver-style base for a Mauser 98 (its lower than the standard Weaver M-98 base). For the rear I used a #55 alloy Weaver base, the same as for an HVA small ring Mauser. They came out to be exactly the same height, parallel with the receiver.

I could go for EAW or other European mounts, but they are generally too high for me.