Rotor keeps arc tracing

Hello,
I'm new to this so bear with me. Thanks ahead of time. I've been through umpteen rotors, several caps, modules, etc. I have an 84 GMC with a mostly stock 305, Edlebrock carb, 10K miles on a "refreshed" motor, rings, bearings, oil pump, etc., emission garb removed, no spark control, etc. It has run poorly and had very poor fuel mileage since I've owned it (15 years) but it's a parts getter so I've put up with it.  I put a dist. in it from Summit...still burns through the rotor. I checked it again and noticed the dist. didn't have the ground tab under the coil...so I put one in it(not sure if it's supposed to have it)....still arcs out on the c/w posts. So again, coil, wires, plugs, cables, grounds, etc. I'm lost.  

Are you saying it had this problem with the original distributor as well as the new one? I assume this is an HEI unit?  

Yes it's an HEI and Yes it's always bunted rotors and has never run right. Being an 84 model it's had its performance problems from the start. It's always idled bad and gas mileage was horrible. I always assumed it was the emission stuff, low timing, etc. The truck has recently gone "emission exempt" because of it's age so I've taken off all of the non-working emission stuff and rerouted the vacuum lines etc. It's simple and right now. But looking back, whenever I'd do a tune up it always had a burned rotor. When the rotor would go bad it was somewhat unnoticeable because of the other issues.  

Check the line voltage on the B+ wire going into the HEI cap.  

I did JW. It's right at 12V. I have a radio shack volt meter, but it shows almost exactly what it showed hooked straight to the battery. I've checked the ground(s) to the block and to the firewall. I put the VOM from the battery negative to the bottom of the dist. and it show almost no resistance. I'm perplexed. I can change the rotor and it will run good for a couple of miles then it will start to slightly miss. A little bit at idle and you can feel it around 2K in park. And it's completely random - not a one cylinder miss. It acts just like it should with a burned rotor.  

As I was rechecking the line voltage wire for 12V (as JW454 suggested)I discovered another wire lollychained to that wire. I believe it's the power wire to the old ESC. Can that be causing the rotor to arc through. I've unplugged it but my brand new coil smells bad. Can the coil be bad and still fire the plugs? The truck still runs bad.  

If it had the same problem with the original setup, we can 99% eliminate distributor internals as a cause. I feel that line voltage is spiking on the b+ wire to the distributor. Just to prove me wrong, temporarily wire a toggle swith to activate ignition power to the distributor and go direct to the battery for a power source. Of course use yet another new rotor and see how that does. If the coil smells burnt then it is almost certain that line voltage is spiking. If voltage is intermittently spiking, look for a problem in the alternator/regulator system. Ever notice the voltmeter jump around?  

By the way, what plugs are you running and what do they look like after being run?  

JW, I appreciate your replies, Thank you. I will do the wire thing that you suggested. I think it's a good idea. I've never seen the volt gauge move (spike). It's the stock gauge. When I tested the voltage to the coil, I took the little cap off and stuck the VOM on the B+ tang to the coil. I reved the motor, held it stead at a higher RPM, thrashed it a couple of times - completely steady. (almost scary steady). I have a yellowish spark. The spark will jump a 1/2" gap - but pop 20 times - miss three. This truck has never stalled or failed to start.
I have mostly run Autolite 26. They have always looked good. A couple of them may have had issues at times, but nothing that jumps out at me. This last time I got parts the kid pulled up AC R143TS on his computer. I stuck them in for now. It's a hotter plug, but it's an old truck so they may be alright. Your thoughts on the new plugs? Do you think my stinky coil is still good?  

If the coil is still firing, it "should" be okay. I was going to say R44TS would be my choice because of heat range and the projected electrode, but Autolite is well known for it's durability. I'm curious to know how you make out, if I can think of anything else, I will surely post. Good luck.  JW.  

Is there a reason that the Summit $89 HEI distributor would have the pole piece indexed differently? Some sort of hot rod application?  

What do you mean by the "pole piece"?  

The piece that goes on the Distributor shaft that rides inside the pick up coil.  

The magnetic pickup? Is that what your referring to? Is it white in color? If thats what your referring to, No they wouldnt be different.  

I believe you are reffering to the reluctor, looks like a 8 pointed star. I have never been inside a Summit HEI, but I wouldn't think it would matter how it was indexed. It would still trigger each time a point intercepted a point, which it is doing, in the fact that it runs.