FI,
If you are serious about a mill that size then boxing the frame would probably be a worthwhile effort. These frames were designed to work with the leaf spring suspension and flex to help absorb some of the forces transmitted by the springs. Since you have already modified the front suspension and have plans for the rear then making the rest of the frame rigid will improve the performance of those components. If almost sounds like you are flying by the seat of your jeans though. Do you have a distinct plan for the frame? Again with the HP/Torque you are planning to have, the running gear needs to be able to handle it or you might wind up in a ditch or around a pole somewhere down the road.
Boxing the frame is pretty simple. Use construction paper to make your templates. Then transfer this to 12 ga or thicker sheetmetal and cut out your pattern. I used my cutting torch and then cleaned up the edges to fit just inside the frame channel. The holes are there to provide access to bed mounting points and other locations where things bolt back onto the frame. They are not just there for appearances so plan their location as needed.
I would think a four link rear with coil overs would be able to keep the axle in place. I do not think leaf springs would be up to that task but other may disagree.
Your schedule seems tight. In order to meet it you probably will need lots of money, no wife or kids, a nice garage, and plenty of time. If you have those things now you probably will not after the fact if you keep to a 12 month plan. Just joking...I hope.
The pics look good. I would definately reinforce the outside of the subframe. If you have not already done so, you will want to test fit the front sheet metal now to ensure the wheels are where you want them. The gas tank I used is out of a 67-69 camaro. I am currently thinking of changing to a 31 gallon tank from a full size blazer for two reasons: 1. more capacity and 2. the width of the camaro tank prevents me from running the exhaust on the sides of the tank. Right now it will have to come under the tank which may be just fine but will make dropping the tank difficult should I have to do that in the future.
Good luck on your project and keep us posted. We like to see other people work.
