I’m running this cam in my 340. It has stock rotating assembly with J heads like yours. Running Air Gap intake and 750 Holley carbrator. Engine made 438 hp on dyno at machine shop. View attachment 1715660534
I think that is the XE275HL cam? I have one of them sitting on the shelf. What kind of work have your heads had? I’d be pretty happy with that hp number from my nearly identical combination.