I've just finished setting up the milling bracket and vice etc on my old lathe, to do some light milling. And I've got some suitable brass bar.

Currently my plan is as follows, but I'd appreciate input from anyone who's done this before.
The designis to be the same as std crosman, for parts interchangeablity - so same bolt/barrel/mounting height etc

cut bar to length, face, centre drill both ends, drill one end for the barrel dia (maybe 1/2 way though), drill the other for the bolt dia (up to the correct distance, just ahead of the small securing screw. this depth will form my reference point
mill top flat for dovetail
cut dovetail (or leave flat to bolt a bit of picatinny rail onto)
cut flat on opposite side around 10mm wide
use round nose (19mm) milling cutter to create the groove that mounts on the cylinder. Critical dimension is the barrel mounting height, dictating depth
mill out the loading area
install the barrel and bolt and determine correct bolt travel
drill from the side the start, end and a couple of mid positions for the bolt slot (horizontal and vertical) and mill out
drill out the TP
drill and tap the barrel grub screw
drill the small mouting screw hole
drill the rear mounting screw hole

I'm expecting a fair bit of trial fitting and fiddling, but I think I can probably manage.

Input welcome,
JB