Mr. Diesel, I don't think you want the 66/14 combo for towing with a 12V. If your gonna be at 400HP you don't need that much charger. I sold a 62/12 to a guy with a 97 dually. He absolutely loves it. He liked it so much that he told me to have anyone that wants to discuss it to call him. He also has the FE. He tows heavy with 4. 10's. If your towing with the FE I would suggest the 2low kit. But at 400HP an OFE would be great. I am sure you need the new flywheel, as the EEP is cast iron(at least they used to be) and is machined for a DD application. I would suggest the 13-1. 375 con OFE if your staying below 450HP, and not sled pulling. It will handle one or two hooks a year at the local fair, but don't expect to leave the line in 4 th low at 4K RPM.
The 13" conversion clutches already have the flywheel machined for a BB pilot. I haven't had anyone complain of a bad bearing yet. Peter has even dropped the core charge on the 13" clutches. It is a lot of clutch for the money difference. You get the updated pilot bearing, a flywheel that you don't have to take to the machine shop and pay $50 to grind it, then another $25 or so to have it machined out for the new bearing. I have a 6 speed 13" already and if I pull out my FE for an OFE, I have thought really hard about buying the 13" ofe for mine for the above reasons.