lovehamer Steve Take a deep breath. We can walk you through this. Valve cover first, Mount the valve cover on the head and remove play on the cover. SHARP BITS. Next Grind the broken bolt threaded end to a point and use this as a center punch to start the hole. You really only need the mark to start in the aluminum. Next Get masking tape and see how depth the hole in the valve cover is until you hit the head. Put the tape on the drill bit leaving just enough room to slide this down the hole for the pilot hole. Put grease on the tape so it doesn't bind up when spinning inside the valve cover hole. Slow Speed on the Drill, aluminum is soft to drill. 3/4" deep should be all you need to do this. If you have the cover tight, your pilot hole is centered. Next get a bit for the correct size to the tap. Use some WD-40 when doing any drilling. Slow spray to cool the bit and keep the chips from sticking to the bit. Blow out the hole and tap it. You will have to eye this for the correct angle for the tap to go in. Put a bolt in one of the other holes and use this for the correct angle. Just take you time and use lube for this too.
Rear main studs. Do you have a wiz wheel grinder? Yes/No? If yesyou ccan cut the main studs in the motor. Just cover the area with paper and tape real good. If you don't want to cut them in the block, remove the studs and cut them in a vise down to the correct size to fit under the
oil pan. Are you using a windage tray? You will need two gaskets. This will take up some room also. If you cut the stud on a vise use wet towels to control the heat from the cutting. You can either get a stud installer or double nut the studs to reinstall in the block Don't touch or wiggy the main cap if you can aviod it. Install the shorter studs, lube and torque to spec. Recheck the work and assembly. Get a friend to help you with this. 4 hands are better than 2.
Rick L