i personally think that's a pretty good cam profile, and if your valve springs can handle that much lift without bouncing then stick with it. it's a little bigger than the tighe stage 3 grind, which is mine and nick's favorite. your cam's only a 272 degree cam, it's not very big at all, i'd say it's about just right for a 4k/5k
ideal AFR is 14.7 for max efficiency, and 12.5 for max power. i think your car runs rich down low in that dyno graph because the primary choke is too big. changing back to a standard aisan is no way to diagnose problems, they run rich anyway and are shithouse at atomising fuel. sounds like you need a new workshop. or twin sidedrafts :P
the single dcoe would probably be an improvement over whatever you have at the moment, even if just for driveability. but i don't think it will be that much of an improvement. look at it this way, you'd spend 700 bucks and have a small improvement, or spend 1500 bucks and have almost perfect carburetion. sure it costs less, but where's the best value for money?
i agree 56rwkw is pretty low for a 5k, stewart's 4k makes 53rwkw. he's using a camtech 609 (In 33-64 Ex 72-32 Lift 0.435). consider rob's engine a 4k, and a pretty oversize 1430cc one at that :D
you usually take 25% for rwd drivetrain losses. or just convert engine kw to rwhp (which is *0.746). 100kw at the engine = ~100hp at the wheels