67 is my favorite year, and also what I own. Its not the origional motor, 302s came out in 68. Its hard to saw without seeing it, but offering 3500 might be good, might wind up paying 4 or 4.5.
1) RUST!!!!! worst area is the cowl, Ford didn't paint inside
pour water over the cowl area and check for a wet carpet.
2)I don't know of any forums that specialize in the 67, but Stangnet has a classic section. You'll be able to find help here too.
3)National Parts Depot has some good performance stuff.