++ About checking Tony Athens for KDP status. (Tony's direct approach some find abrasive, but uncontested expert). There's also some information on the idler pulley bolt & changing to a larger bolt. I did it, EZPZ. Ditto the CPL #, any 6BT advice will be predicated on that. I also had problems with the Sherwood M71 pump, still have it, but my engine is keel-cooled. I did change the mixer with a re-design that worked better with the limited flow on the pump, DeAngelo's in FtL can help with that, they've done a number of them that incorporate the design changes that I asked them to implement. My exhaust hose was running well over 250F, muffler was heat damaged. Now it's about 95-100, depending. MUCH improved.
Boatdiesel.com is a great resource as well.