Pulled the Mess that was my Timing Chain....

I am with RRR on this one; it is best to pull the cam. If you drill in place, the metal chips are going to be difficult to keep out of the engine. And, some precision is needed in the drilling, and the cam is going to walk back into the engine on you as you drill. Not doing this part well will put you right back where you are.

Besides, you have done most of the hard part of getting to the cam already: the front timing cover. The most rest is easy, and you need to pull the valve cover anyway on car that has not had good maintenance to adjust the valves and inspect up top.

When you pull the lifters, make sure that you keep them in EXACT order, front to back. Get a box with compartments (an egg carton is good) and number them 1 to 12. Mixing existing lifters is pretty much a guarantee of some wiped out cam lobes. I also keep the pushrods in order too.

I almost forgot that you have to pull the oil pump out part way and the distributor. The distributor is easy; the oil pump can take some judicious prying to pop the pump and gasket loose. And getting it free of the block can be a hassle; read Pishta's recent work to R&R the oil pump.

If you drill and tap 3 smaller bolt holes in the cam sprocket and cam face, try to get at least 1/4" grade 8 bolts in there; you might need allen head bolts to fit well. And use flat and lock washers on each; SAE flat washers are narrower and may fit better in the cam sprocket's front recess. Use Locktite on the bolt(s) regardless of which way you go; clean out all the oil before applying Locktite.