[R-390] Need some R-390 info please

[Phil M.]

I brought a Motorola R-390 home from the Belton TX hamfest and
need some info on what are apparently depot mods.  First, at the
top of the front panel above the id tag are two lines...

MWO-11-5820-294-35/1
MWO-11-5820-294-35/2

On the back panel, a bnc jack has been added with a small wire
connecting it to the diode load terminal on the barrier strip.  Also,
the antenna relay has been removed and replaced with a metal
panel with a multi-pin military style Amphenol connector and an
N-connector for the antenna.  The Amphenol connector pins are
wired to a terminal board mounted on the inside of the back panel
and this panel contains 6 top hat style diodes.  Does anyone
know the purpose of this last mod?

thanks, Phil