Mike Jones has a grind specifically for the motorhome big block engines. It ain't cheap, but you get what you pay for. If I was to make one change other than what you have mentioned it would be the cam. The smallest lunati voodoo would be a distant second choice.
No more than you will be driving it though there is nothing wrong with keeping the oem cam if it is in good shape. Won't get quite the same power but it will be well above what the 318 was on its best day anyway.
Trans cooler and shift kit would be on my list as well. OEM low stall converter is good for this application. It will help keep the revs down and give a little better mileage since it is likely not a lock up converter.
How do I find out about Mike Jones? Did a search and the commonality of his name about put Google into a tailspin...
