Have you tried turning the engine over by hand?Maybe something is binding causing the starter to labor.

If the engine still cranks with difficulty with two plugs out, pull the other plugs. The engine should spin freely. Ensure that there is no actual binding before proceeding with the other checks...

Let's start boiling this thing down.

First get it to crank WITH THE PLUGS IN and the ignition disabled. The ignition may be kicking back due to a number of reasons:

Too far advanced

Crossfire/ wrong firing order

Something crossfireing in the cap/rotor (tracking)

Problem with the ignition/ pickup causing multiple / off time/ erratic firing.

If you have no1 cables, and they are properly made up, they should not be the trouble

If the #4 engine to body ground is properly made, IT should be OK.

Pay attention to the cable heating--if it's near the end terminals, that may be an indication of poor end termination/ internal corrosion.

You PROBABLY don't have "2 bad starters" but it CAN happen--you buying 'rebuilts?'

At this point I would also suspect the battery. Find some "old guy" with a legitimate carbon pile type tester--not the new fangled fake ones that you can carry in one hand. REAL carbon pile testers probably weigh at least 15 lbs. This is what you need to test starter draw and other tests.

I would certainly get "comfortable" with a wrench on the engine balancer and see how much friction drag (no plugs) IE does the engine turn by hand OK?

OK, 1 problem down, 1 to go
The slow/labored starter problem turned out to be a bad firewall ground. The connections were tight but the firewall connection had some white crap (buffing compound? from the recent body shop visit) under it. I moved the engine-to-firewall ground strap to a better location and that solved the slow starting problem.

Tomorrow, I'm going to retard the timing and see if it will fire.

I really appreciate all the replies. Thanks!

Now if someone could do something about Ike....

!!! MAN !!! Glad to see some progress