thats cool, my conversion was 90% easier because I learned from what others had done previously.
A local shop should be able to build a tank to your specs.
During my research I found they make standard size cores and side tanks pretty much throughout the industry, so they all build similar sizes and shapes.
The BII core support accepted a Nascar standard Ford layout radiator tank, this cut the cost down considerably because Ron Davis, who built mine, didnt have to re-invent the wheel, they just had to customize a tank they already built.
The Explorer core support should not be any different.
My tank is 6" wider then the AA or Duff conversion radiator (same unit, made by AA, Duff is cheaper) I was able to fit it simply by cutting 2" of sheet metal per side from my stock core support and of couse fabricating mounting brackets.
I supplied Ron Davis with an AutoCAD drawing, it got faxed back and forth a few times for coordination, then when the unit arrived it was EXACTLY what I had drawn. This also allowed me to prepare the truck for the unit while they built it.