> So, who in the group offers their services for performing module
> modifications like this

Well, I'd love to be able to offer an opinion based on knowledge of
the circuit, and then who knows, possibly a suggestion for a mod or
two. Unfortunately the 155 is among the modules I don't possess, so
if anyone out there has traced the circuit (this takes dedication,
especially on something of the 155's size!) or has access to the
schematic and is willing to share it, I'll happily spend some time
looking at what makes it tick.

If the main switching logic is something like a 4024 counter driving
a 4051 analogue multiplexer (someone who has one could seek out these
nos. on the chips ), then Florian's suggestions for changing the
clock direction might be reasonably straightforward. If the circuit
is of this form, then this also suggests to me a (conceptually) easy
way to make it random - feed separate random sequences (like a slowed
down 117) to the 3 control pins on the 4051. It might even be
possible to do this with just one shift register producing the random
sequence, rather than three separate ones. But without seeing the
schematic, this is pure conjecture...

Tim