The mystery of my intermittent spark is solved.  Thank you to all of those who made suggestions, as it helped get to the bottom of the issue.
This morning I decided to repeat the test I made yesterday hooking the starter to a separate spare battery that I had.

This time I removed both the large cables going to the starter and engine block ground.  That way, I didn't have to mess with a jumper cable.  I hooked up the battery, turned the master on and engaged the starter.  To my utter amazement the spark was intermittent again.  I thought thgat certainly I hadn't made a mistake yesterday an imagined that the spark was good on a separate starting battery.  After some swearing, I thought about yesterdays test, and the only thing different was the ground cable.  So, I removed the ground cable from the battery,and hooked up a jumper cable from the negative terminal of the battery, and hooked it up to the reduction drive plate, as I had done yesterday.   Cranked the starter and had good spark.  Did it twice, just to make sure.

What the **** !

So, I decided to connect the jumper cable to the ground cable end, instead of clamping it the the reduction drive plate.  Cranked the starter, and had intermittent spark again.  Somewhat amazed, but onto something here.

I measured the cable (0 gauge multi-strand silicone) with the Fluke meter, and it showed pretty much zero ohms.  I measured from the spot on the front engine housing where I had the ground bolted on to the reduction plate, and measured about 3 tenths of an ohm.

Since my original installation, I always had the ground cabled bolted to the front housing, with a bolt into one of the tapped holes where the air conditioner mount was.  It is a pretty large bolt, and I never suspected that, considering all of the bolts that hold the engine together, and the many bolts that hold the reduction drive plate, that there would be any issue.  Boy was I wrong.

I reconnected the cables to the main battery, instead of the spare battery, and instead of bolting the negative cable back on, I used the jumper cable to connect to the reduction plate again.  Perfect spark !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

My current ground cable isn't long enough to reach from the battery to the mounting plate.  I found the cable that I had left, and I have plenty of spare cable, but I don't have any more of the lugs for the ends, so I will have to order some.  I am going to attach to ground inder one of the mounting bolts for the starter. Regards and thanks for the help,

Steve Brooks