HP71B plastic vs. metal back

[rprosperi]

The early 71B's had the metal back, but it was changed to the plastic back style some time in 1986, unrelated to other changes (e.g. ROM version) so it probably was simply a cost-savings industrial design change.

I know that some parts are not compatible between the older and newer design, however I'm not certain if the display components are affected, but other experts should comment within a day or so.