FE = Ford Engine.
OP - can you send more information / specifics / pictures of this car?
Do you have a link to the for sale ad?
All FE engines look the same on the outside (from a 332 to a 428) so it's not difficult to pass off, say, a 390 as a 428.
Nobody in there right mind would adapt a C4 to an FE engine when the C6s are still readily available.
Why the confusion on the year of the car? Is it a 65 or a 66? Is the seller being upfront with you on every aspect of this car?
The VIN and/or the data plate information will go a long way towards clearing things up.
Do yourself a favor and make sure you get the whole story before proceeding with the purchase. Only saying this because, based on your descriptions so far, something smells fishy.
Good luck.