I can tell you this, if it's a PEEC engine(electronic) tell him you'll denounce your friendship if he doesn't replace the pump with a mechanical one. The PEEC was Cat's first electronic truck engine, it still had the mechanical pump groups and timing advance, but they were controlled with brushless torque motors instead of mechanical linkage, springs, etc. The list of issues they had is too long to type and even if you fix it correctly it doesn't last, she'll be back in a couple months. The Cat ET program will usually communicate with it, but it's best to use the ECAPs.
Now onto the studs. Don't try to do battle with the thermostat housing throughout the whole job; get some gaskets(maybe a new regulator/seal while you're at it), drain the coolant and get it out of the way. Get some solid M35 cobalt drill bits or M42 if you have the finesse not to snap one, and they will drill right out. They're not hard. Drill it as close to center and straight as you can until you see a shadow of a thread. Swap to a 1/4" carbide burr bit and go around the hole until you see threads all the way around and use a pick and a tap to pull the threads of the broken stud out. I've done this literally hundreds of times on Cat heads and I very rarely need a helicoil or insert. DO NOT tap the threads all the way to the bottom of the hole!!! Cat uses taperlock studs that get snugged up in the hole before mounting the manifold and they'll thread in too deep if you bottom-tap it.
Fuel pressure isn't critical on those. 30psi. will run but they usually have more than that. Oh, and if it's a PEEC and he doesn't want to spend the money to convert it, let it be known that you told him on(give the date/time) that he was going to go into the poorhouse buying things like replacement BTM's, transducers and sensors. They pop 'em like candy and still cry like a spoiled brat.
