HEI no spark issue on older 70’s 350 sb

Car: 81′ El Camino
Engine: 71′ 350 SB that came out of a Corvette

Hello everyone I’ve been attempting to help a friend get his car running again. After a HEI upgrade that he purchased from O’Reilly’s auto parts. Now first off I’ll tell you he bought the distributor ,Wires, and plugs while having another person that was going to install everything and evidently that person ended up not being able to get the car running , and blamed the distributor, saying it was somehow accidently burned out. So the owner asked me for help . When I went over to the car. I looked over the distributor which showed no obvious visual issues of being burnt out! But he said he had a lifetime guarantee on the part and just to rule out any problems with it . We went and exchanged the part for a another brand new distributor /rotor,cap, coil all included.
Salesman asked what the vehicle it was for and I told him the 71 Corvette 350 is what it would be installed on. He said it didn’t show it would be compatible with that engine . But I thought that would be because of the year and HEI hadn’t been invented or wasn’t offered yet on that car engine. Ok so.. I’ve gone through static timing this thing numerous times trying to get this car running bringing the engine over to TDC on the compression stroke. Then dropping the dizzy in with the vacuum advance pointed to about cyl 6 and the rotor pointing to cyl 1. As well as the number 1 tower on the cap.
I’ve verified 12.volts on the ignition wire that plugs into the caps (Bat) position. The car has no tach so that’s empty. No spark at all checking the plugs ground against the block. So then I went and got new ground battery cables. To go from battery to the block ,and block to the frame ,battery to the chassis ,and two ground straps from the back of the block to the firewall. Still no spark at all. I then tested the ignition wire under start conditions and found the voltage drops from 12volts to about 10volts when cranking. So I then made up a test 10 gauge wire straight from battery to the (bat) position on the cap. Still no spark at all. Im at a loss and really stumped as to why I can’t get spark out of this distributor. I also want to add. That at one point the owner had left the key in the on position and I didn’t realize it. Then removed the cap and as I started lifting the cap I heard electrical arcing from the cap center button arcing to the rotor. So I know there is power into the distributor it’s just not coming out of the distributor. I’ve haven’t done any tests of anything inside the distributor only cause it’s brand new and I’m experiencing the same issues that the other person that was trying to install the first distributor was having which tells me that chances are that distributor that I returned was probably just fine. So the chances of 2 brand new distributors being bad are slim to none. I can’t think of anything else that could cause this. And I am very confident in my abilities to do this job and have done it many times in the past without issue.i mean even if I was off on the timing (which I’m very certain I am not) it should still spark. It would just be erotic or backfire or what ever . And I got zero spark at all. After installing new grounds I verified the distributor is grounded to the body of the dizzy checks out good. Please does anybody have any ideas as to what could be wrong? All help would deffenitlly help me sleep at night as this is stuck in my head trying to figure out.
Thanks