you've made a grave error, the series front axle was never meant to be driven on hard tarmac. hence why a series is PART TIME 4wd. Wehn you lock the diff to make the vehicle move you are causing wear to the front axle and the steering knocking is not the steering box it is the UJs kicking inside the axle as they transfer the drive.
A coiler is FULLTIME 4wd and will have both axles powered when on tarmac, central diff unlocked.
If I were you, i'd be looking at rebuilding the front axle and converting the LT230 to PART TIME 4wd. i'd also give myself a slap round the head!