Have one in our 03 Winnebago. Put close to 4,000 miles on it pulling a toad in the Black Hills and Yellowstone a few months ago. Engine runs great. I haven't had a heat problem with plug wires put did have an exhaust manifold leak. Installed a set of exhaust header last month to fix that problem. Again it depends on the buildup whether you'll have any heat related problems. Both Fords and Chevy's have had heat issues in the past. Not necessarily related to the engine but the motorhome surrounding them, think airflow.
GM stopped building Big Block engines for production vehicles several years ago. They do make big blocks for marine use and performance engines. Parts are available and it's a good combo with the Allison trans.
The Ford V10 is a good engine put I wanted the 8.1 with the Allison. The V10 will do the job but you have to wind the heck out of it to get the job done. It's just a different design and requires a lot higher RPM than the 8.1l to develop the HP. If you don't mind listening to the V10 scream when pulling a grade it's a good engine.
