Before doing any panel glueing also check out 3M Automotive and Durobond products (now owned by 3M). Lord has much the same products, but I've never used them. Similar to the Lord product line, there are at least 3 different formulations that you can use for metal-to-metal (not counting the plastic-to-metal options). The differences are in open time (before set up, allow panel adjustments) and most importantly structural vs, non-structural. The structural stuff is strong enough for pillar and body bracing, and is used by the big 3 in a lot of highly stressed places. This stuff is stronger than spot welds and comparable to a fully welded seam.
Also watch how much grinding and sanding into the bond area is going to be required. You don't want to bond, then grind away a good part of your strength, then get a crack after panel finishing.
The most common panel adhesives are readily available from body/paint supply houses, and a few web ecommerce sites as well. I'd pass on JB weld for serious bodywork.