If i had to place a bet on which W.W. Aristostigmat had better coverage, i would choose the f/9 version instead of the latter f/6.3 one.
I could be wrong though, as i don't remember if the f/9 has the same optical layout.
Arne Croell reports about Meyer LF lenses in his document about post-WWII easter block optics, but the f/9 version was abandoned by then.
There are a few missing informations in that very interesting document:
1) the 80mm W.W. Aristostigmat is missing from the list
2) some barrel lenses have cells that can be fitted in shutters of the same vintage: i own an uncoated WW Aristostigmat 16cm f/6.3, which goes in a Compur No.2 shutter (from a 240mm convertible Symmar), keeping a perfect spacing.

The f/9 version had some more focals, so they could fill a few gaps in the f/6.3 line. I was not aware that many of them were sold in shutter, i thought that the vast majority of them were sold in barrel.
A. Croell estimates the coverage of the f/6.3 version as 90 degrees at f/22.
My 16cm covers 8x10" with some movements. So the f/9 could cover 95 degrees, which should be enough to cover the format , with no room to spare.

Did you check the reflections on your 135mm?
Is it a double gauss?

have fun

CJ