When I first rebuilt my truck in 1998 I bought about half the 60-66 specific parts from American Classic, and the other half from Chevy Duty (now Classicparts).
http://www.classicparts.com/Both are reasonably priced and provide quality parts and excellent service. Several years ago American Classic instituted a minimum order policy, so they lost my small order business. Now I buy virtually all my 60-66 unique parts from Classicparts. I’ve also purchased a couple of Corvette parts from Eckler’s. They are very expensive, but have top quality products that sometimes cannot be sourced anywhere else, and offer excellent customer service.
From what I’ve seen Brothers and LMC are the price leaders, charging more than anyone else by a wide margin. The only item I’ve purchased from LMC was their clear dome light, since they make it and it cannot be obtained anywhere else. The item was excellent and order processing on my order was good. Unfortunately I’ve read many threads in the truck forums that complain LMC has the worst customer service available, and many of the parts they sell are offshore brands with significant quality issues. I’m not sure this last issue is fair, since I think most suppliers get their parts from the same limited manufacturers.
I’d suggest obtaining a catalog from each of the suppliers (many/most are free), and compare prices (or compare online) for any items you want to purchase. That’s what I did before I started spending most of my money with Classicparts. In my experience they are almost always the least expensive and I’ve never had an order or quality problem with them. I receive email specials from Bob’s, but even their sale pricing is about half way between LMC and Classicparts, so I haven’t been able to buy anything from them to determine how they do. Here are the links for Eckler’s and Bob’s:
http://www.ecklerstrucks.com/http://www.bobschevytrucks.com/It would also help if you live close enough to any of the suppliers (or they attend a car show in your area) to go look at their parts before buying to determine the quality level of parts they offer.