[Hallicrafters] SX-71 Run dates?

[Julian Bunn]

I've just finished replacing the BFO coil assembly on my SX-71, and while I was
about it I measured the values of the capacitors connected to it, and replaced
a couple with more modern types and closer values to spec..

I noticed that the resistor between the BFO tube and the BFO switch was a
100K value, whereas the Sams Photofact circuit I was looking at showed it 
should be 22K.

So I looked at the other circuit diagram I have, part of a copy of an original
SX-71 manual, and on that circuit it was marked as 100K. This diagram is labelled
"RUN 4". In fact there are a few minor differences between the diagrams (not to
mention the layout, which is radically different).

I thus assume my SX-71 is a Run 4 (or greater?) version. Does anyone know what
the differences were between the various runs, how many there were, and the dates
of each?

Thanks!
Julian