Good link, thanks.
I was looking at '86 with 6.9 under 100K miles, one owner truck...

 

I know you would.
I need to figure out a way to do it /without/ a mill, using cheap portable tools, because then I can do it for very little cost and effort.

Realistically, I see no reason not to be able to do it with a special fixture - a drill bushing will hold the drill extremely precisely(I've done this, repeating within a couple of thou), and unless I was using a carbide drill, the drillbit will flex as it is.

I just need a piloted drillbit so it follows the current hole down, something to keep me straight, some cutting oil and a drill.

Plus, if I can do what I expect I can do, I can sell DIY kits for doing this that will be far cheaper than a set of ARP studs., and stronger too.