If your WLA is early 1943 it will have engine number 42WLA**** and case (belly) numbers 42-335.
Case numbers for each model year started September 1st,so case numbers 42-335 would be the 335th pair of 45" cases machined from September 1st 1941.
From 1942-45 there were 7 types of WLA,all with engine number starting 42WLA.
If you give the first two digits of engine number with stars for the remaining numbers (42WLA52**) and the case numbers,I may be able to pin it down more.
I Looked it again and correct belly no. is 43-*335. By Palmer´s book (How...military...) my bike´s engine no. refers to type III and that engine-number range ends at april 1943 (page 69). I also understood from his book that this belly no. is for case that was machined and stamped 1943 and ready for assembly (page 9).
Check Your pm.