Check the welds front and rear, all my old style svi mags are starting to crack at the welds and spreading. This with the fact that most of the mags were filed on the sides so the base pad would fit gives you more internal room side to side.
I used a taccom 3 barrel before they sold the aluminium shroud barrel they now sell for my template. The barrel was 7 " or 8" long and had a steel shroud with holes in the shroud. I ran the aluminium shroud back to the extension. The barrel with the aluminium shroud comes in at 13.5 oz and I have no idea how to do and post pictures.
I run a slide mounted docter sight on a slide machined for the sight. The docter sight mounts on the slide with out any shims but it uses a small felt circle under the battery to put pressure the battery . If the screws and pins line up it should work.