The two inch difference between fenderwells for a 65 to a 67 is enough to make the big block into an early A quite an undertaking. Exhaust is a big hurdle to clear. We custom built headers which was a long trial and error process. The distributor up front is one plus though. The additional weight for a big block is just enough to be a noticable con as well. With the power and torque available from a stroked small block (which is almost a bolt in swap) I would recommend that route unless you just can't get past a strong desire to have a big block