The early engine crankcase differs from later types with regard to the camshaft trough. The Spitfire cam will fit, bearing bush sizes etc are all the same, but the lobes may catch on the crankcase. Later engines have a wider trough.
More important is attention to the crankshaft, the big end bearings are supplied with oil via a cross drilling, the so called sludge trap. This is accessed by removing the two screwed in plugs. No if's or buts, this is the most important aspect of ensuring a trouble free rebuild. Lots on the forum and YouTube. As we say they can be real bastards to get out. With the plugs removed the oilway needs to be cleared of accumulated carbon, sludge etc and given a good wash through. Another oilway leads up from the timing side journal, This can be cleared at the same time.
I reckon a copy of Roy Bacon's book "BSA Twin Restoration" will help identifying parts and time spent reading previous posts on engine building will save a lot of hassle.
The attached pictures tell the story....
Swarfy.