I think the first thing I would do is a head swap to the 308 casting , ported of course , they seem to make a lot more power than the X or J casting , I am working on a similar combo 360 here we were using the 484 Mopar cam & swapped to a Ultradyne solid cam with similar duration & a lot more lift , we used the 284/558 grind & oddly gained nothing , , I have been thinking about what cam to try next , obviously the extra lift isn`t helping so we need to increase duration & overlap so I htink we need to be in the mid 290 * range where you are but not sure what lift to go with , I was thinking of trying the Mopar .557 grind solid cam or possibly the circle track .540 ? grind from Mopar