It could be a clutch that engages the spindle gear with the stud gear out to
the rest of the change gearing.

The lathe is in the "modern" configuration for gearing, having the leadscrew
and feed rod combined.
I don't recall from the pics, but you will have to find the left-end bearing
box for the leadscrew (right end is still there), and with that the
brackets/setup to get the gear set on the end of the leadscrew meshing with
the
rest of the change-gear train.
Looks like it does not have power cross feed, only power long.
Frank Morrison

I have all the parts, they're just buried in these boxes. It seems to be
complete.

That lever's more than a clutch. It's marked 1, 2, 3 and on each setting gives
the gears a different ratio. There are two external gears that connect to
whatever's in the headstock. One's driven by the stud gear off the spindle, the
other is output. Three distinct speeds on the output gear. It then drives the
rest of the system. The latching F/N/R tumbler lever disengages the drive
train.

It does have power crossfeed, through a setup like an SB9. Either/or long/cross
with a clutch.

GTO(John)