Presumably the engine is either a 60102 or an 80102, since those seem to have been the standard engines for the SB45 after the Kirby Lauson phase was finally over. I think both have the same bore but different strokes (i.e. same cylinder/crankcase, different crankshaft) so the obvious way to check which you have would be by measuring the stroke, using the old pencil-through-the-sparkplug-hole trick. However as you said, Joe Carroll probably has both engines ready to hand, and a detailed knowledge of the differences between them.
