Engine Ground to frame and body?
Corrosion at firewall fuseblock connection? (sorry, think you said you cleaned this already-put some dielectric grease on contacts to pevent further problems)
Reverse lockout switch circuitry, connections, or adjustment of linkage or no linkage causing column to lose contact intermitently.
The battery is grounded directly to the engine block via water pump bolt and there is a wire from the negative battery post to the front right fender.
I do not have a ground strap from the engine to the body.
Either you are not reading correctly or do not understsand. It does not matter how many wires are running from the Neg. terminal to the block. The block needs to be grounded to the frame and body.
I had a 70 Camaro work car BITD. It had some "issues" starting intermittently. I got put on 2nd shift and coming home one night I notice a flash of light coming from under the console. Upon further inspection, I realize the engine was grounding (arcing) through the automatic shifter cable. Hooked up firewall ground straps and problem solved. Check out fundamental issues first, like proper grounding and connections. I will add, if where the ground cable is connected to water pump bolt, there is paint, rust, no washers, corrosion etc...this will cause a lot of problems. I had a diesel that had starter issues. It turned out that it was drawing too many amps. Enough to heat up the pos. connector stud on solenoid to a point, causing the nut to loosen after several starts.