I can help sort some of this out and maybe get it to the point where the guys that know stuff can help.
The first GM HEIs came out around 1975. They had small distributer caps. The big ones came a few years later around '80-'81'. All of them fit the 194-292 series engines and with care can be fitted to the older sixes.
The engine doesn't care which hole on the cap the #1 plug wire is in as long as the rotor is pointed at it when the spark arrives. The other wires have to be place in the firing order in a clockwise direction around the cap. If you've never seen a real clock that is a right hand direction as in tightening a bolt.
There are lots of ways to determine which hole is #1. The easiest, if you have not turned the engine since you took the old distributer out is to put the old distributer back in. Make sure the tang on the shaft is in the slot that drives the oil pump. It will not seat to the block if the tang and slot do not alined. At this point you can be in the right place or 180 degrees out. (1/2 turn) If you did not remove the plug wires they may help you to see if this is right or if you need to pull it and turn it 1/2 turn. If you can find where only one of wires fits you can see if the rest will fit our to the shape and length of the wires. Mark it and install the new distributer and use your marks to run the wires.
If you have removed the wires or turned the engine it is a bit more work but not bad. Go ahead and stick the new Distributer in. Pull #1 spark plug and turn the engine until #1 piston is coming up on a compression stroke. It will be blowing pressure out of the hole because both valves will be closed. Whichever distributer post the rotor is pointing at will be #1. Wire from there and time as necessary. Good luck.
