I would suggest replacing the porcelin with polymer insulators and increase the airspace.
Check with Hastings or S&C for the polymer types and ratings.
240v 3Phase is a Delta connection which has a power leg.
There are 2 conductors which measure 120v phase-ground and 240v phase-phase, the power leg will measure 208v phase-ground. You can split off a 120v single phase supply by tapping one of the 120v lines and provide a continuous neutral.