340 Max HP Potential with X/J heads?

From what I gather, the 915 J's aren't going to flow much different than the eddys once ported so I've gone ahead and bought them for $300. They are untouched from factory from a 71 360. Im in Australia and there aren't any machine shops that are familiar with what I need to do to them now to get them to their 90% potential so I need specifics to tetll my machinist exactly what to do to them. Thanks for the help! I'll post a new thread with this question to maybe get some different ideas.

I mean, if they've ever ported a set of heads off any old American 2-valve pushrod V8 the same basic rules apply. I don't think there's much specific to Mopar heads compared to Chevy or Ford small blocks that makes porting them different than the others... Mopar heads just have better port shapes, valve angle etc. from the factory than the Brand X stuff