You will need to used the lines from your mechanical pump, the end of the line that attaches to the pump is different on the DB4 pumps. All you really need to do is pull the pump and lines off of your current motor and swap it over, the steel part of the return line, just after the pump, where the inj. connect to is different also, I used my original part here. You want to be careful when you pull your lines as they have a coating on the inside and being ~30 yrs old it can come loose if the lines are bent, clogging your inj.
I was thinking of buying one of the "drop ins" I would do lots of research on the companies out there selling these at what look like bargain prices. I wont name any specific companies, but some seem to be VERY problematic from reviews. I do know that if you want to spend the money, Kennedy and Peninsular
are both excellent places but they are also pricey!
In the end, I chose to rebuild my own, it cost a little more than the "drop ins" you see but less than the two places I did mention and I know it was done right with quality parts. The crank is one thing you want to watch out for, almost all the "drop ins" have machined cranks. GM says that because of the nitride coating on these cranks that they should not be machined. I've also heard of mis-matched or wrong size bearings and such. One re builder will offer a warranty, and I believe will even offer help with the labor on a warranty claim, but do you want to have to go through that?
On your "how to" if you go with one of the remans, you want to specify that you want the mechanical inj. and I personally would stick with the V belts, the V belt and serpentine setups use different water pumps. That is just a personal choice thing, I don't like the serpentine belt, its kinda like putting all your eggs in one basket. I know it can be done, but I am not sure what all is required to go serpentine w the dual alts.
As far as fuel dilvery, I went with an elect. pump, just a factory replacement for a 93 I think truck. There is a skid plate on the pass. side where there are some rubber lines above, I located my pump there, put an inline filter in before it, wire and fuse the pump in an ignition on hot spot in the fuse box and there ya go! Makes priming a breeze too! On my M1008, right under the fire wall, there is a brass "T" where the fuel line from the tank stops, then another piece of steel line is run to the mechanical pump. since I went electric, I just replaced that line from the "T", straight up the fire wall to the filter.
If you go factory turbo setup, the oil return for the turbo goes where your mechanical pump currently is.
As far as the batteries go, I am using the front mount as the base for my new one, just cut a piece of plate the correct size, tack it on and there you go. You could fit two batteries on the front base as it sits, but the tabs and up turned edges of the base would be supporting the weight of the batteries, I did not like that idea. I will build a new top piece, along the same lines as the original, maybe even using it, just cutting it and tack in the needed pieces to make it long enough for two.
I will for sure let you know how the fuel tank project goes, that is a ways down the road though. I plan on using all factory components, I already have the valve and switch, I will just get a new tank and straps and I believe it will bolt right in. The guy who is doing my cab corners said if I could find a truck in a salvage yard that has the area around the filler door in good shape, I could cut it out and he would be able to cut a hole in my current bedside and weld it in place. I'm not sure how hard its going to be to find a diesel to get the area from, the filler necks are diesel specific.
I am also going to be rebuilding my injectors and will be posting on that, w pics. That will be sometime after new years.
I hope this helps some, again, please feel free to ask if there is anything I or the other posters have not answered.
Good luck!
Greg