340 TC

At least do a compression test.
Cylinder pressure at your elevation is very important, and
with 3.55s it is possible to have less performance with a big cammed 340 than with a properly built 318. Or at least you might be very disappointed. This is because a big cammed 340 with low-compression, may not come alive until AFTER 4500rpm/about 42mph in first gear. A stock teener could be making pretty good power and performance up to about that same rpm,and so the performance difference between the two, up to 42 mph COULD be pretty similar
The compression test may lead to a cam swap
Remember; you said the PO pulled it because it wasn't enough for him; it may be a poor combo. You would be very disappointed to find that out after the install.
The compression test will tell you a lot.

On an unknown engine I would also do a LeakDown test