The non-speedlock 52s have the long knurled knob on the rear of the striker similar to the Krag and 1903, while the later speedlock versions are much shorter at the rear of the striker. AFAIK the stocks are similar if not identical and the original target stock can be slimmed down to a very pleasing shape, doesn't take much, it's fairly slim already. The B models are marked B but I've never seen an early 52 with the A marking, don't know if the A was ever used as a mark on a rifle. I've done several 52 sporters, they require almost as much alteration as many CF rifles for best appearance and ergonomics but the result is truly outstanding!
Regards, Joe