It's a bizzarre code as it doubles up on the 'V'
The VB310 part is obvious enough, but the suffix VRM breaks down as
V= Panel van
R= 2 door
M= Australia

I had believed that B310's were imported while local production capacity was used in the manufacture of the larger P810 & P910 series of cars. Can anyone verify?

It used the H150 rear end. I don't think that the Borg Warner was seen on anything other than the locally built B210 [120Y] sedans from July 1976 untill the end of 120Y production.
The same happened with the P810. A Borg Warner rear axle was introduced in about '78 or '79, but the following model P910 Bluebird did not use it at all & it had the H165 & H190 diffs instead.