I've used GMCPaul and ClassicHeartBeat both with great customer service. Just my .02 but to me customer service and quality parts will win out in the long run over a lower purchase price. Both these vendors KNOW these trucks and have a vast amount of knowledge which they will share.
Also, you might want to consider becoming a dues paying member. Best $25 a year you will ever spend on your truck. Then you will be able to place WTB (want to buy), F/S (for sale) and WTT (want to trade) ads in the suitable parts forums. Quite handy when needing items you can't find or have spare parts from a build you would like to turn for $$ to buy other needed parts. When I was restoring my '71 4x4, before I found this site, it was quite a challenge finding correct parts for a vintage 4x4. They are NON-EXISTENT in salvage yards for sure.
Good luck and Happy Truck Building,
