Welcome along, somewhat unfortunate to say the least.
BSA kept to the same design of crank for the post 1950 A7 engine, it shares the same main and big end bearings as the early A10.
If you keep the existing con rods, get them checked for ovality of the big end eye and for straightness. Big end nuts and bolts changed threads over the years, a failure point is the wrong thread nut on the bolt....and from this horror story a likely cause, along with mechanical ignorance and RIVET MAN mentality*
Plenty on the Forum about crank grinding, main bearings, sludge trap cleaning.... a marginal at best design in these earlier engines and when clogged up the cause of major engine failure.
Wear limit is 2 Thou ovality on big end journals, BSA Service Sheet 207 (find in Forum Literature Section) gives standard regrind undersizes.
Metal Spraying is an established technique for restoring worn components. Cost is usually the decider, and while alternative parts are still available, a replacement crank is far less hassle. Even though worn, your damaged crank still has a value, so don't just dump it. As stated that big nut on the crank needs to be up nice and tight, 65/70 Ft Lbs, plenty on the forum about this and setting crank end float, which is critical for a smooth running motor.
Swarfy.
* Known as RM a character from Worty and Berger's similar engine " bought restored" (er not!) and valiant rebuild saga against the odds. Features the savior MWAS.
