Not real experienced with the Magnums.
Are you running a governed engine or open RPM?
I will assume it is governed somewhere around 4000RPM. If this is the case remember, these are nearly the stock specifications and the engineers that built it knew what they were doing. You just want to tighten things up a little to account for you running good quality fuel, not overheating it and keeping good oil in it. These are things the engineers could not count on.
Are these engines even firing? In other words do the cylinders fire exactly opposite each other? If they do not then I recommend 2-2 exhaust, not a 2-1. The scavenging will not be right on an odd firing engine. If they are even firing, then the 2-1 is the way to go. Longer is probably better at the low rpm (within reason........ Single pipes around 18" before collector)
Adjust valves as tight as you can without taking the risk of hot valves not sealing. In other words, just a skinch tighter than the bottom of the stock specs. If they are too tight it will cost you a lot of hp, if they are not tight enough it will only cost you a tiny bit of hp.
Ignition timing should be advanced a bit from stock. I don't believe in the "Advance it till it detonates then back it off" theory, Just go a couple degrees more than the stock specs and run good pump gas.
The #30 carb is a good idea.
If the cooling fins are bolted on the flywheel then remove them, you wont run it long enough to overheat.
Also remove the stator if you don't mind charging your battery once in a while.
Do not run race gas.
Do not advance the timing to the point of detonation (if that's even possible on these engines).
Do not listen to anyone, myself included, without first reading your rule book and the rulebooks of all the clubs near you first. (Rules tend to drift across local clubs eventually, you don't want to build something that is illegal or non-competitive in a year or two.)
The most hp is to be found in a good valve job, machine the heads (correctly) and get a cam ground for the RPMs you are running. All this other stuff is just baby steps, but they do help.
Most importantly, make sure you don't build the fun out of it. If you want zero maintenance, leave it mostly stock, just tuned correctly.
Too often people try to build a hot rod and end up with maintenance they don't enjoy, or they cant handle it when they still get beat. Make it fun, and be a good sport.