the 385 series is the big block, so it would be a 429 cu in and not so good on gas. expect 10 in town and 14 on the highway..but, it's a muscle car!
or it could be a stroked out 351w and a real hotrod! either way it sounds like a fun car..
[Ford 351 Stroker Kit, 351 Windsor, 383, 393, 408, 418, 427, 454, Stroker]