A lot of late model vehicles use a positive offset wheel to allow the suspension members to be set further outboard to gain suspension room with unibody construction, engine compartment room for all the modern induction systems, accessories and pollution controls. Negative offset was popular years ago to allow drum brakes to be in the air stream for cooling and with racers to gain room for wider tires with separate frame and leaf spring cars. It's a lot easier to roll, radius, or flare the fenders than to tub the frame.

 

Here's the power pack. It measures about 27,5" in overall width and close to 24" height. Length is didn't measure very closely but somewhere in the 28-30" region.

I changed my mind regarding to the horsepower level (at first) and will go standard with some mods like long tube headers, 3" exhaust, K&N air filters and aftermarket ECU. This should give me about 600hp/500ft.lbs at the crank.



Mercedes Benz 63 AMG engine 6.2L 32v

 

One option I haven't seen mentioned for the rear, is 3" wider rear fenders. That would give you an additional 6 inches of room, and simplify tire selection, as well as eliminate the need for gigantic tubs, frame modifications and loss of bed space.
I'm running 10 inch wide wheels with 265 50 15 BFG tires (11.5 inches wide to the sidewall) on my 53 with a 60" wide 9 inch housing, (At the axle flange) and the tires are outside the edge of the fender by 1/2".

If 3 inches more tire on each side isn't enough to keep traction, you'll be my new Hero.

There are a ton of manufacturers out there for these, this is just one I found with a quick search.

53-72 Rear Fender - RH - Fiberglass - Stepside - 3" wider

 

3" wider fenders is actually mentioned on the previous page. I've ordered up a Currie Enterprises Ford 9" housing kit with axle tubes and ends so I'll probably make up a 61-62" wide rear axle and use the wide fenders. I don't want to make room for fender wells in the bed so that's the better option. Since I let go of my supercharger plan I guess I'll be able to fit wide enough tires to get some traction with the power pack Just hope the power pack fits though, it should since the HEMIs are bigger.