Yup. local machine shop. The difference is whether the holes are exactly perpendicular to the intake mount surface (LA) or whether they are 45* to it as the Magnum intake bolts are.
I did not call hughes up and ask about inserts to make up for where the threads are thin (IDK if it was/is some sort of "trade secret" or somethin) but there was someone here that had made a homemade jig to do the mod "at home", I guess he sold it or loaned it out and "POOF" it is gone. No one that I have ever heard of has ever mentioned whether they Heli coiled the holes or anything but i have seen/heard of many making this mod with no mention of it.
I have a Magnum block on the stand, I am gonna mock up the heads on there and set the intake on with the side gaskets to see that the holes will line up the way they should before I pull the old ones off my truck.
As I said I had this done at a "regular" machine shop not an automotive one. The local automotive one does not have a suitable mill (they DO resurface heads and flywheels but that is not the kind of mill you need) or clamps/blocking, to set up/support the head in the correct position to drill them the way they need to be.
Whatever you do, DO NOT torque that intake to standard LA intake torque specs!!!!Magnum specs will do the job.

I am using my daily driver truck as a "guinea pig" of sorts, if this one turns out well I may put a set of Magnum heads on my 78 Fury (also a 318) before I pull it out for the season.

BTW; I am using the original 1983 318 cam as the Magnums have a higher (1.6 vs LA 1.5) rocker ratio so that will wake up a stock cam, even if only a little.
For a carb, I am using a Carter AFB (elec choke version) NOT an Edelbrock version (using what I have here) not sure whether I will go with the 500 or the 625 version yet though. No diff because, the venturis and butterflies on the primary side are the same on these carbs according to the Carter carb books I have; the difference is all on the Secondary side; so theroetically if I don't get into the "back half" of the carb it should run exactly the same, with either one. I do have (2) Carter "Strip Kits" here to play around with various jets and metering rods on it.

Once I get it back running and the bugs out, I may experiment with one of the Holley 4360's I have laying here(450 CFM 4 BBL Economaster)