I think any 460 or 454 will do well with the addition of headers, FF muffler and a CAI. Both run hot and have a tendency to crack exhaust manifolds especially when pulling long hills with a tow on a hot day. Headers will not only give you about 80 more HP for pulling hills but reduce the heat generated and reduce the constant downshifting and fan clucth noise you have now. Also you can add another layer of insulation to the inside of the doghouse to reduce the noise and heat. These mods all helped me with my older 454. Also look at your towing capacity for your MH it is probably 5000 lbs, but a lighter car would be better something under 3000 lbs. Does the MH run hot now on hills without a tow?