High Plains - Can you confirm the dimensions on your brakes? Front shoe size? Rear size? I've got a 1984 NAPA Brake System Parts Catalog that lists your C40 front brake shoes as 11-5/32" x 2-3/4" and the rear shoes as 15" x 4".
The catalog lists the front brake shoes set as either Bendix 248R or Raybestos 248R. Both of those can be found through a web search and appear readily available. NAPA actually currently lists them as:
NAPA Fleet 248R - Riveted style* or
NAPA Fleet 248 - Bonded style*
* NAPA does not list the C40 as using this brake shoe in their online content, but my catalog confirms they fit 1960-65 C40 trucks.
The catalog lists the rear shoe sets as Bendix 108 or Raybestos 108**. Neither of these is currently listed on the current NAPA web site. A web search found nothing available new or in old stocks being sold on line that I could find.
** The catalog list these same rear shoe set numbers as fitting 1958-65 C50 and 1960-65 C60 trucks.
As with most of the Big Bolt trucks, rear shoes are more or less commercial truck size/grade. Your best bet for getting them back up to snuff is take them to a commercial truck shop and have them relined. They will have the right materials and skills to get the job done.
As far as the return springs go, my NAPA catalog lists the return springs (axle set) as NAPA 80169 for front and rear. The original front brake pull back springs are listed as GM# 3694822 (primary) and GM# 3739278 (secondary). The rear brake pull back springs were originally listed as GM# 3748513, but were replaced by GM# 3799320. You can still find some of these rear springs offered like these
ebay NOS GM# 3799320 springs.
Hope this provides some help with your questions.
PS - The catalog also lists hydraulic brake components (boosters, master & wheel cylinders, flex brake hoses and axle bearings/seal #'s) if you need more info.
