If You go from a run of the mill Magnum lobe to a fairly aggressive Mopar lobe, it could be worth 15-25hp on a 225 easy. But with the long pushrods, and requisite spring loads, stock components are out. Better pushrods are always a good idea on tall-deck Slantys anyways, but may not be in the original budget plan. Springs should always be so, it's a matter of degree & related cost, but expected. I'll try to link My post in Steve's spring shimming thread, about My project.
Post in thread '340 xhead spring shimming, height and pocket question(s)'
340 xhead spring shimming, height and pocket question(s)