I'd go big block unless you plan on towing ALOT and have the budget for a Cummins conversion done the right way. All the money you save will pay for a lot of gas and you can get your project going sooner.
Are your drip rails shaved off?
Reinforcing it is a good idea. I'll probably buy a new brace kit too as the one on that side is unscrewed and bent.reinforce that edge because it's gonna buckle again otherwise. And, close it from the side and not the front.
I thought Josh meant when fixing it, ha. Makes more sense now.