Thanks for the photo's. You've got some work to do!
I think the primary cases are going to be very hard to find. A temporary fix is to use a steel outer primary cover as used in early 30's Ariels. AJS and Norton are close / similar.
If the trunk is the petrol tank, I don't think it's repro.
I hope you can find a crank assembly. At worst, if you can find the mainshafts, you might be able to have the rest made up.
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.