For testing only, yes, mounting them opposite would be appropriate.
But, VASIMR engines are due to be tested at ISS soon, arent they? Provided that they work as expected, turning this module into a useful orbit to orbit transport vehicle, (perhaps LEO to LLO and return, with big payloads?) would be the first thing I’d want to do.
It would seem to be a no-brainer to mount hinges and swivel points, and begin operation.
if memory serves, VASIMR VX-200 are ~300 kg each; 80 tonnes of propellant is plenty for pulling bulk supplies to/from lunar orbit.
