Thanks for replying, jh4321.
Vepr 12 has a rail on the cover that wouldn't be usable in a bullpup, it's too far back.
I hadn't thought of that. I just assumed the IZ models had the same rail cover placement as the VEPRs and was a non-issue. Glad I asked.
What reasons would one have to want to use a Vepr 12 over a Saiga 12 in a bullpup kit?
Reliability. I've heard nothing but mediocrity from Saigas, especially the un-modded ones, while the VEPRs haven't really had any common problems - and that's out of the box.
I am not sure if a mag well would work on kush but if it could and you wanted the Vepr-12 for the magwell go with the Izzy that has the magwell built in instead. I wouldn't do the vepr 12 in a bullpup.
According to the Kushnapup website, it's compatible with the magwell models. The big concern is the trigger location. I think my best bet may be the IZ-433
The vepr-12 is a cool shotty, but IMO it is a heavy shotty and is cool for a regular full length beast.
I'm still in research mode and am leaning towards the Remington 870 BPU. Much more reliable than any other bulpup (conversion or native) shotgun.