Hi Tony ....A few dimensions that might get you pointed in the right general direction .
Generally speaking , the dimensions casings seem to have limits of at least some + or - ,005" or so , for not too critical stuff like the breach housings , but more critical areas will have much closer tolerances , and be classed into high and low bracket fits (this not concerning us right now) .
Inside dimensions probably being more critical than outside as this is where it all goes on .
I'm measuring in Imperial Inches as I just happen to have a vernier caliper of that type handy right now ...( but you can easily conv.to Metric.)
Starting at the front of the breach , just ahead of the feed block , the nominal thickness of the sides is about ,120" ..(But for about 1/2" Sq where the top cover pin passes through , and where this is ,205" thick .)
The Rear side plates Aft of the vertical riveted joint are nominally ,104" thick .
The INSIDE FACES of the ,120" thick walled Front ( machined from forging) section , and the Rear ,104" thick side plates ARE PRETTY EXACTLY FLUSH , such that you cant even "feel" the inside joint .
( Internal parts slide and work etc. in this INNER area and the inside of the breach Needs to be flat for smooth operation ....The "Joggle" joint is to the Outside ).
The Riveted Joint:- The Front section thickens up on the Outside face via a radius of about ,10" (estimate) , from its original ,120" by an additional ,070" which would give a thickness of ,190" over the last ,550" of its length .......However , this thickened " vertical strip" is recessed on the Inside face , by a depth of ,104" and length of ,475 " , in order to accept the ,104" thick Rear side plates , which recess into the front part by the amount of ,475" and the FRont and Rear sections are joined here by rivets , which are Csk inside and outside ....The vertical C/L of the rivets seems to be about ,26 forward of the rearmost vertical edge of the joggled front section ...(difficult to see in this light , with the flush riveting and aged surface etc.
Inside each of the rear side plates , just Aft of feed block , are the guide cams which control the movement of the "lock "...These may well be ,146" thick pieces , added on somehow to the inside faces ,and bring their over all thickness to ,25" thick at this point .. (rather than the side plates being machined from ,25" plate ).
At the rear , where the cocking levers reciprocate back and forward in its 1,03" high cut away recess / slot ; .....The area , on Each side plate Outside , top & bottom ,...is thickened up to give a longer lasting sliding surface .
This is done by riveting on (& ?sweating ? ) small ,08" thick plates , so increasing these areas to nominal ,184" thickness ...These additions each are of 1,94 long and ,43" high and ,08" thick .(except the LH lower * )
After afixing , these were machined to give a recess 1, 255/1,29" high ,with the newly formed lands thickness (was ,184) now being ,140" for the reciprocating sliding blocks to bear/slide on .
These ,08" additional bearing surface plates (fitted to upper & lower lands on each outer side plate slot ) , have side profile on the RH plate of rectangular form with 4 off ,20" radii on the 4 respective outer corners ...Similar on the LH side , but modified on the top rear corner to fit the top profile of the fusee cover ....and the lower one is longer , being extended rearwards * to include the rear lower "wedge" latch , that locks the back of the fussee cover in place ...( the upper wedge being integral to the rear " Butt plate" ) .
The bottom , inverted " channel" section cover plate is riveted on to become the integral base of the receiver ...Rivets C/sk on the outside only ....All fits between joints , and csk riveting are very well done and can only just be seen in good light ....but cannot be felt !
Hope this is of some help for you , I'm afraid I couldn't get a sketched sorted out due to a slight problem on the server right now .
Regards John .
PS Thanks also Tony , for you comments also on my FE2b thread , which I haven't yet had time to update .
Feed Block ....This was a forging or a casting and was machined by use of Milling , use of shaper * , and broaches , as far as I can tell .
* (Not same machine as that which you guys in USA call a woodworking spindle moulder .....but could roughly be described as like a pivoting vertical lathe tool on a "Ram" arm .)