I've had good luck with FP kits, never had a problem with IPD kits but are lesser quality IMO. At one point I worked at an Navistar parts dealer for 8 years, rebuilt way too many 466/530E, occasionally 466 mechanical, one had the head rebuilt at a machine shop with OEM valves (made in Mexico) 2 weeks later it dropped one, broke at the keeper groove, Navistar suggested we use aftermarket, I believe they were Melling.. 6 of 1 half a dozen of the other!
I strongly suggest you turn this kitty into a complete monster, just because you can! Maybe find a B model, build it over the winter, 7-800 Horse 2500-3000 Torque??