First, I would be very sure I have a 390 and not a 360 in a 76. As long as you know what you have, fine, but more were 360s than 390s.
Assuming its a 390, you could go cheap at first, at least if you think you can get the top exhaust manifold bolts out. Headers, duals, a crossover and good mufflers, rear gears, a shift kit, and a recurved distributor will make a huge difference before going inside, and is likely even worth it if it turned out to be a 360
Also keep in mind it will take a little more money to buy headers that fit a truck with a set of Edelbrocks or TFS compared to stock heads, but, if the bolts are all going to break, may as well just bite the bullet for heads an intake and a 600 Holley and a set of FPAs for a CJ .
As far as the cam, I wouldn't start buying until you see how deep in the hole the pistons are and calculate compression.
All that being said, a distributor with a healthy advance curve, a shift kit to bang the gears, more gear in the rear, and a free flowing exhaust with a bark will make it more fun, and if it runs real nice, you never have to go inside. I have even run that combo with a 500 Holley 2 barrel for a little more breathing