Anthony,
Of all the lathes I have come across and had to machine, they all went fairly smoothly. The metal is usually easily machined cast iron, and that can usually be worked on with hand tools, electric drills etc, that saves on trying to get the bed onto a machine for drilling. That is of course if you don't need reccesses and things cutting out, but again, depending how adept you are at drilling and filing, even that can be done accurately by hand, and a cheapo die grinder helps a lot in that department.
For marking out such things, I have a large collection of transfer punches. Get someone to help hold the part in position, then feed the punch thru a hole and give the end a tap. That puts the punch mark for drilling your first hole. Drill and tap the hole and mount the part up, making sure it is in the correct position, then repeat with a transfer punch for all the other holes. I find I can get things spot on that way, easily within a couple of thou. I mounted my DRO read heads by doing it that way, and when checked out with a DTI, they were spot on. You always have a bit of fiddle factor anyway, the bolts usually have a bit of play in the holes they go thru.
It is very difficult giving advice like this because at this time, it has to be just general stuff. When you actually get the job in hand, then by looking at it, more accurate information can be forthcoming.
Like I tell most people, if you get stuck, and you can get the part to me and aren't in too much of a rush, I don't mind helping out. There is always something in my shop requiring machining or fixing that isn't mine.
John