You have a 2 1/2-3 ton. Later 400 Series used a 302 engine but yours is probably smaller. I'll look it up tomorrow and let you know.

All older GM trucks are LH thread on the left (Driver) side and RH on the right side.

Try eBay Motors for manuals. The other recommendation for Old GMC Trucks is your best bet.

Until you can find a GM manual get hold of an old Edition of The Motor Truck Repair Manual. These are always on eBay for around $20, you shouldn't have to pay any more than this unless it is in pristine condition. There are plenty of them. I think approximately Editions 5-8 cover your truck. Ask the seller to tell you specifically what GMC years are covered. I'll also look that up for you tomorrow.

These are GREAT trucks.


'31 Chevy 1 1/2 ton,
'42 GMC 2 1/2 ton 6x4,
'52 GMC 2 1/2 ton 6x6,
'53 GMC 5 ton