The pics are my rear-mounted parting-off tool. The upright is a casting
from Metal Lathe Accessories. The curious round knob on the front is
where one would mount the casting if using a lathe with a lantern-style 
tool-post. The casting is mounted to a 3/8" cold-rolled steel plate about
4" X 4 1/2" with four tee nuts in the corners spaced to fit the cross-
slide.  The upright is approx. 2" X 2 1/8" in cross-section. The base plate 
is dowel pinned and screwed to the upright. 
 
Almost any rectilinear piece of fairly rigid material could be used for the
upright. If you wanted to use the parting blade directly in the upright,
instead of in a holder, steel, case or through hardened, would be advisable.
 
I have a recurring job that involves making special, threaded studs. Because
there is a long bar of 3/4" material sticking out the left end of the spindle, it's
very awkward making belt changes for the threading and parting-off portions
of the job. The rear-mount tool lets me run the entire job at 1000 RPM. (!)