Here you see the gun mount clipped onto the bolt, and the shoulder rests being prepared. Bend thick copper wire to the sizes shown on the plan.
It is easier to solder if you hold the rests in a couple of drilled holes as shown.
Add a couple of ammo drums from 1/4" brass tube. They can be packed with filler before painting....
...and test the complete gun out for size. It should fit a 1:48 figure nicely.
The torpedoes are made from odd scraps of 1/8" balsa.
Note the kink in the copper wire - it will stop the wire rotating.
This is the simplest lathe I have seen!
Any drill can be used so long as it has a Slow speed - perhaps 500rpm. Hold the drill and the wooden block to the workbench with clamps - though a half-brick will do at a pinch! Just keep the speed slow...
Glue and clamp enough blanks together to make a 1/2" thickness on all sides.
And here is a basic torpedo shape.
Now solder the supporting arm to the rests.
Cut the torpedo racks out of 0.1" styrene using a round file to make the 'hook' shape as on the plan.
And here are a couple of blanks waiting for shaping. Check that the copper wires are each on the central axis.