That's true with everything. You'll probably be fussing with this for years. (LOL)
There is evidently a book (in German only, and rare and made of unobtainium) which includes plans of one of the guns. There are also a couple of highly informative, if prematurely aborted, SBSs which provide some interesting insights into the kit. Otherwise, there's the internet (and its pitfalls) and a Squadron (I think) book on rail guns for material. There is a picture of Hitler viewing the gun, not likely at Stalingrad, if the photo is even real. To that end, I scooped a 1/35 Mercedes G4 (6-wheeled) limo (complete with figure) for a concept I'm mulling over.
I like an element of the unusual if I can work it in.
I understand that the kit's plastic doesn't lend itself to conventional styrene glue and cements. Was that your experience?