The higher pressure systems are indeed needed for efi set ups; your mechanical pump should work fine provided that 1) the diesel tank has an appropriate sump/pick up assembly in it (if it has an in-tank pump, you'll have to get rid of that); and 2) you get all the diesel fuel/deposits that have built up over the years out of the tank and lines from front to rear. I've not done a diesel fuel swap so I don't know how difficult that is. I do know that small low pressure electric pumps can be mounted at the rear by the tank; that approach is very inexpensive, and it almost totally solves any potential vapor lock issues because the fuel line is under pressure all the way from the rear. A lot of vapor lock issues occur because it's so easy (with just a little heat in the engine compartment) to vaporize fuel on the suction side of the mechanical pump.

You'll need to be sure the tank is safely vented (air must be able to get in or you'll pull a vacuum on the tank deforming it, or worse). And if the diesel system had a return line you'll need to deal with that.