Points were the world standard for 80 years, so if hooked up right it should start. Normally on older Fords the ignition run position only provides about 7 volts and a full 12 volts is required to start. A wire from starter solenoid to coil provides a full 12 volts when starting, but only remains hot while starter is engaged. If run constantly at 12 volts, the coil overheats and fails.

HEI will be hotter spark and less maintenance, but won't work without sufficient voltage either. IDK your truck year, but some had a separate ballast resistor thru which 12 volts was reduced to 7 with ignition switch in run position. Later on, Ford installed a resistor wire, so it isn't really noticeable visually, but still cuts current down to 7 volts.

I had a similar problem with a 73 Mustang, would only fire but not start because it was only getting the 7 volts in start position due to 2nd wire from solenoid to coil not hooked up. Once it got the full 12 volts it started immediately.

if cam is too big and it is bleeding compression, the rocker stands can be shimmed or shorter pushrods installed. But, I think you are on the right track generally with inadequate spark. I believe the HEI needs a full 12 volts also though.. And points will work fine too, if you have 12 volts to coil on start and 7 volts on run.

When you said you swapped everything from Dads truck, I wasn't sure if that included distributor. So thought it also may have been swapped already. If same distributor was in it and working but doesn't now, were the points replaced? Any chance they are partially grounding due to defective fiber washers or assembly order? Or bad condenser?

I had an old Dodge recently where multiple guys could not figure why with new wires, points, cap, rotor it still had no spark. A wire inside distributor was hooked up wrong and grounding the hot to points. Fixed that and it started. This truck has some spark though, so probably unlikely.

On another board, a guy with a rebuilt early FE installed his new timing set along with a spacer that was behind the original cam gear. Problem was the replacement gears have that spacer cast into it. So, with the equivalent of two spacers in it, it pulled the whole cam forward (no cam retaining plate on early FE..). It ran roughly for a short while but messed up lifters, cam, twisted the oil pump shaft and wrecked a new distributor. Motor had to be torn down again due to metallic shavings and roll pin sheared on distributor and some of its parts missing... Hopefully your truck has a later FE.

HEI is better, but points should work fine unless some component is defective, or it isn't set up right. But as you say, those possibilities shoul both have been eliminated upon HEI install. Doubt the back 2 cylinders mean much since if spark is real weak it probably couldn't burn all the fuel that tends to go to the rearmost cylinders and the spark at plugs is likely inadequate in all cylinders. I have started motors with two cylinders disabled, so the 2 wetter plugs is likely just a symptom of weak spark at the plug in all the cylinders and gravity.

Assume points are gapped ok, not burnt from sitting closed with key on, are contacting square and no oil or grease is on the contacts? Have seen people get lube on contacts when lubing the little rubbing block and it really inhibits the spark.

Some replacement point sets today aren't very well made. But even if great when assembled, if key was left on w/o engine running any length of time, that can burn the contacts. One of the point system weaknesses the HEI is more tolerant of...