Here is a URL to some photos of the Gustav/Dora railway gun.
http://www.kent.k12.wa.us/staff/trobinso/physicspages/POpart2/po2002/Schwerer/pictures.html
I saw an HO scale (1/87th) on the web for a mere $650.00.
My current build is Trumpeter's Leopold. Right now, I'm almost finished with the suspension, brakes, and wheels on one of the two rail cars. Many small parts but,
the smallest I've used so far are the individual oil caps on the wheel bearings.
Sorry no pix available yet and, it may be a while. My company is transferring me from
Sunnyvale, Ca. to Boulder, Colorado so my work area will be coming down shortly.
Ray