- Regelbau 607 -
The Regelbau program was a project by Germany in the second world war. It was a series of standardized bunkers designed to be built in large numbers in the Siegfried line and the Atlantic Wall. There were multiple strength levels at which these bunkers could be built, with the 607 being level B (2.0 meter thick walls) and being primarily designed for the army(Heere). The 607 was a "Munitionsunterstand II", or bunker for ammunition storage 2. It could store:
2.160.000 rounds for MG
7920 rounds for 3.7, 4.7 and 5cm KwK
2520 rounds for 7.5 cm
2496 rounds for 10.5 cm
3136 cartridges for 10.5 cm
660 shells for 15 cm
225 cartridges for 15 cm
450 cartridges and shells for 17 cm

- Schematic -
The schematic itself is made in 1.16.5, but I can also recommend using this in 1.7.10. This version sadly doesn't have "clean" stone stairs and slabs, but you can fix this with mods like Staircraft and Slabcraft. These mods also work really well with these schematics:
McHeli mod
McHeli German WW2 content pack

If you have any tips don't hesitate to tell me in the comments!