Alright......I want to help you so badly, I am gonna be a glutton for punishment and try ONE MORE TIME.
As stated multiple times, an engine is a self powered air pump. The more efficient it is, the more air it moves and the more power it makes. As you start making more power by adding high performance items such as big carburetors, intake manifolds, bigger cams and headers, you need to exponentially grow the exhaust system.
Here's why.
A high performance engine moves a LOT of air at a high velocity. That air exits at a very high velocity as exhaust. As the exhaust enters the headers, it picks up speed because it is still partially burning and because the headers 4 seperate tubes on each bank provide a reversion free (pretty much) path for the exhaust to exit the engine.
Reversion is the tendency of exhaust to want to flow back into the cylinder after combustion. What you have in your particular situation is a HUGE reversion issue. The reason is because your exhaust is 1) too small and 2) crushed on top of being too small. That engine is trying to pump probably three or four times the amount of exhaust into the exhaust system than it can scavenge, thus, you have a HUGE amount of back pressure, causing exhaust reversion. This reversion means burned exhaust is contaminating your cylinders on each and every combustion cycle and making power fall WAY off.
This leads to why this engine runs "so poorly" compared to "the other one". "The other one" was nowhere near the power level of your present engine, so, the exhaust.......even though in bad shape, could better handle the job the milder engine gave it. So, even though you have a "better" engine now, it is being choked to death by a small exhaust system that is crushed as well, plus, a smaller than needed carburetor.
Yes, I can see 100 HP loss here with all your problems combined. Even though your engine is "mismatched", it COULD make a TON more power just by fixing the exhaust, putting a bigger carburetor and finally sorting out the timing curve.
If you cannot understand that explanation and still continue to argue, then I honestly believe you are beyond help.
