IP related adjustments that you can do. Fuel inlet on IP, remove fuel inlet steel line to adjust hex 'bolt' under it about 1/8 - 1/4 turn in. This is the IP internal transfer pump and changes the timing curve and charges the plungers more from higher pressure. This can make the IP want to make the engine take off without much throttle change at higher RPM's: still controllable just strange. Be careful as lift pump pressure from the electric lift pump can affect the IP housing pressure as well as the IP transfer pump pressure is referenced off the inlet fuel line.
Light load retard/advance lever on the side of the IP. More advance at light throttle and less timing as the throttle advances via the lever moving. You have more heat at higher load and the diesel lights faster so less advance is needed.
The fuel screw is well documented, but, don't forget the throttle is an RPM request not a straight fuel control. The governor decides how much fuel to give you with the throttle change. So the pump can go fuel fuel for a small throttle change causing smoke if the screw is too far in. 'Smoke puff limiters' are available for Ford DB2's and may work on GM. Regardless this is why the throttle is tricky to operate to keep smoke down.
Lift pump ideal is a Walbro FRB-5. You don't want more than ~7PSI at the DB2 IP.
These are the easy available adjustments to the IP. Your mileage may vary.
What he is trying to explain to you are the easiest adjustments for the fuel delivery of the IP. The leaf spring screw, the housing charge pressure screw, and to compensate for the change in timing curve with increased housing pressure, the adjustment of the timing advance/retard lever on the side of the pump. This is all very good information and has been quite well documented , just need to search more and you will find it.
The slotted bolt holes which you are talking about is the timing of the pump in relation to the rest of the motor. What is being offered to you is what you asked for, how to get more fuel out of a DB2 pump.
The leaf spring screw, allows for longer plunger travel = more fuel.
The increased charge pressure (IP has internal transfer pump to control housing pressure , which in turn controls internal timing of IP) means the plungers will fill with more pressure = more fuel.
The DB2 IP's are also internally timing adjusted with the throttle, using a cam plate lever assembly on the opposite side of the throttle assembly. When lever is pushed in timing will be retarded. Adjustment here is needed to compensate for the increase in housing pressure through the rear fuel inlet housing. As the housing pressure increases, timing advances internally in the pump.....need to compensate for this.
The slots you see on the front of the pump housing, only time pump in relation to motor. The stuff you are being offered here are methodes to flow more fuel with the DB series pumps.....