I appreciate all the helpful replies.
The generator is 142 cu ft per hour, 3.9 gph, 10-12 in water column. So would that be 355,000 btu? Let's call is 70 feet from main tank to generator supply, to add some footage for turning pipe down then back up. The regulator (2nd stage) is right at the location where it comes up out of the ground, about 5 feet from where the generator will sit.
Some suggested a new, dedicated regulator for the genset. This would be where the 3/4" comes up out of the ground into a T. If that is done, the existing regulator is in place for the pipe in the other direction-- going to a water heater 15 feet away. I don't have the btu's handy, but its a typical 40 gal gas water heater.
I don't know how you set line pressure. Does the propane company do that? Obviously, if increasing the line pressure makes running the genset possible, that is hugely more attractive than trenching!!