You will only get 2400 watts from the 20 amp receptacle, if you want to utilize the maximum output of the generator us the 30 amp outlet. I have the same generator and it runs 2 of the heaters you spec’ed out without issue. Make a pigtail that goes from the 30 amp outlet to the typical 20 amp receptacle.
Good luck!
Do try this
i was able to do more than 2700VA on a Champion 3000 inverter genset running A/C at 105* F
and yes you MIGHT need to adjust the voltage regulator and the HZ
adjust HZ by adjusting the governor spring on the carb throttle arm
set that 62hz unloaded a meter but no electric loads
then check the unloaded voltage 122-124 is about right for unloaded
