Electrical or ignition, does not explain why is seems to stall in the 3600 rpm range, struggling to get on the chip, but when it does get through it comes on up to 4600rpm. Nor is it likely the converter. People run super tight converters all the time with not huge HP motors, if they are heavy nitrous motors or similar. Struggling to get on the brake is nearly always a carb calibration issue. Doesn't matter that he tried two carbs. If both have similar calibrations, they will have similar issues.

I recently worked on an EFI nitrous car with a 865in motor. He said when you put it on the brake, it struggled to get there, but when you turned it loose, the motor stayed at 3600 and would come no further. Sounded like it was on a rev limiter. He was convinced it was the ignition box, ECU, plug wires, broken converter, whatever..........with me telling him the whole time, that is was the fuel tune. He messed with this thing for 3 months and changed everything on the car. When I finally saw it in person, it did EXACTLY as he said. When he turned the button loose, it sounded like it was on a limiter and the rpm flat lined on the graph at 3600 and would go no further. He could step off a little and get back in it and it came up fine. I told him again it was the tune........NO WAY was the response.....OK. I finally went over there and snatched the laptop out of his hands and put 25% fuel in it, at THAT rpm range and told him to try it. Did the same thing and "SEE" was his response........Hold on a damn minute, I told him........LOL! So then I removed THAT 25% fuel in that range, plus another 25% more and told him to try it. Came up like a champ and revved to the moon when he cut it loose. Handed him the laptop and told him to now go "fix" the Tune in that area. So why did I relate that story.........because to me, Al's issue seems fuel related. Too much or not enough in that rpm range, for the combo of air flow, converter and other parts he has