Seems fair. The 340 was standard on the 68 Formula S, the 383, rated @ 300 hp was an option. Found white book that shows engine code is 62. Rare? According to Govier there were 64 shipped.
I've been researching the this car as well. 64 total conv. 383-S's, 40 4-speeds and 24 auto's.... There's one on ebay right now, priced high for a non-numbers, non-running, in need of much help car.....