Looking for help in NJ

That seems like a lot of money for a used engine / trans with questionable miles and condition.

The other issues you have is "what is" that 318 out of? If it's out of a truck or motorhome, you'll have to swap your 273 oil pan and oil pickup or find a "car" 318 pan. You'll have to transfer your 273 engine brackets, and possibly the manifolds, again, depending on what the 318 came out of.

If you use / don't use your original transmission, other troubles.

I believe the original 65 trans is cable shift, and the one advertised surely is not The CL might be a 727 or a 904, so the kickdown might be different.

Also, early engines had a much smaller torque converter snout than later models

In other words, if you can't find someone who is knowledgable, this could be a problem