Nourish, there are probably few folks on this forum with first hand knowledge of the mix'n match possibilities of these early frames and brakes. The early Longstoke Parts List are available in the Forum Literature section, but before 1949/50 were published in a format to include all current models, so it will be a real test of character to wade through the information. At least you can compare what fits what. These lists have the individual parts well illustrated, rather than the exploded schematics of later publications.
The rear wheel hubs of rigid, plunger and early S/A models have the same drive splines and wheel bearings, so the wheels will fit, custom spacers may be required depending on the frame used. As noted, plunger hubs have two bearing retainers, S/A just one. The basic pressings are the same, just machined for one or two retainers. Dust cover is more convex on a plunger hub, flat on S/A, so you can tell the wheels apart with a quick glance. Later A65 type can also be adapted, and can run a rear speedo drive, which brings the option of a cheaper modern speedo, rather than the gold standard chronometric type.
The chainwheels are slightly different. They are similar, but have subtle differences for the unwary. As duTch says, the plunger spindle goes through the axle stub, which is bigger O.D. than the S/A type. This requires a larger bearing for the rigid/plunger chainwheel, so the center is machined out larger to suit. The S/A hub bearing is the same as the wheel bearings. Drumside boss on the plunger chainwheel is rounded, S/A has a sharper edge, smaller central hole.
Anything is possible, whatever the choice of parts they can be made to fit with a bit of thought, skill and a machine shop.
Swarfy.