Aus Spec MA61's had W58, alloy sandwich plate (maybe *some* rare with steal)
Singapore Spec MA61's had W57
Jap Spec MA61's had W58
(I'm sure there are some variances of the above 2)
GA61's had W55, W57 or W58
MA70's had W58's with steel sandwich plate. This was NA versions.
GA70's had W58's with steel sandwich plate, some probably had W55's too.
I'm sure MA70's after 1988 had 7MGE's, but they probably weren't imported to Aus after 1988.