[JThiessen]

Since you and I are doing the same thing right now, some details that I see as tough to overcome:
1) Replacing the rails. The rails taper up and in the back on the bottom (I believe the front is just a taper inboard). This taper interfaces with the bulkhead support/mounting plate. Nailing this part down will be tough via reverse engineering. Not impossible though. This is the only reason I have chosen to keep the stock rails.

2) I also think the three part chassis might prove to have too many joints over time. I really think that having a continuous member from front to back is very critical to the flex and structural rigidity of the chassis.