Far too much conversion loss, and way too RUbe Goldberg. (NOT That there's necessarily anything wrong with that...) You turn gasoline or diesel fuel into rotational energy at a loss (thermal mostly), then convert the rotational energy into electricity at a loss, then the electricty BACK into rotational energy at a loss, just to turn the compresor head.
If you have the engine running, you turn the compressor head direct to the engine and cut out all the other conversion losses - the only reason to be running an electric compressor is when you don't want to run the prime mover yourself, you buy the energy off the grid.
The smart way is to get the Constant Run Unloader assembly from Quincy, which will involve a special head with pistons to hold the intake valves open to eliminate pumping losses. And a second air cylinder that drops the engine back to idle when the head is unloaded.
And if there is ever a call for electricity out in the field, say to run a Sawzall for pruning, or flood lights for that 2 AM repair work, you get a small belt-drive alternator head (1 KW to 5 KW) and belt it in parallel with the compressor. (And delete or bypass the idle control when you want power and air at the same time.)
They sell these commercially, search for "air and power" combo.
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