if you are lucky there is stil a build sheet under/behind your seat. otherwise there is no way to tell.
the v8 does use a shorter gas pedal lever on the firewall side, that might be your only clue.
since there is no way to tell for sure, all 63-66's were available with a 283 3bbl , if it was ordered with a v8. some were special ordered with a 327, but every "327" 60-66 I have bought , or looked at turned out to be a 283.
you can have the seller send you the #'s from the front right pad in front of the cylinder head, that will give you the year and type of engine... for example I looked up the "327"
in my 66 and it turned out to be a 66 283 2bbl california smog motor, which was further proved by the still original pass. side exhaust manifold that had the air ports.