Gentlemen,
while I really appreciate and admire your dedication to the finest principles of restoration, I think you could be justified in replacing dodgy brake drums on a number of grounds:
1 They're consumables. Had the truck remained in service it would be on its fourth set by now...
2 it's reversible. Remove and retain - that is, preserve - the present drums, and wear away a set of replacements instead, and if you want to you can always reinstate them. BS7913 recognises this as an entirely acceptable conservation approach.
3. Look after yourselves. Brake failure through a cracked, broken or even simply distorted drum won't do you any good, and frankly I want to read about the next restoration rather than reports of broken limbs, or worse
4. Look after your public and fellow enthusiasts. Brake failure could conceivably result in collision with nasty consequences...
Your choice of course: just setting out an option that might be further consideredi. Keep up the great work
cheers
Will