No choke at all and running at 1500rpm...albeit with blow at header end..
suspect vacuum leaks fair few pipes crudly plugged around air cleaner and carb...its loud...brap brap brap. Theres no flange at either header end or start of centre sections and prior clamps real tight that has ovalised, absolute pig to get the new reducer pipe on and the headers back on the studs...will need a bit more work possibly a flexi..
Vac leaks won't cause fast idle but will cause rough idle. get the motor warm then turn the idle speed dpwn to about 900 rpm. Turn the mixture screw until the motor almost dies then rotate back 3/4 turn. That's a baseline then you can fine tune it back to around 750 rpm when you've cleaned the carb and chased any vac leaks.
As for exhaust, a lot of aftermarket header systems were slip on joints and clamps. I think Doulble S did a system with flanges IIRC. In fact, if you contact Double S, they will still supply you with that system today.
