Old Herbrand Tool for pulling heads off Flathead V8's.

[Flathead21]

Hi Guy's.
Got this old time tool set from an old time mechanic who said it was for pulling off the stuck on heads on Flathead V8's; but he didn't know much more about it.
There are 2 pairs of long studs. One pair of long studs is threaded for 18mm sparkplug thread on the end; & the other pair of long studs are 14mm sparkplug thread. I guess you screw a pair of long studs into the plug hole on the head; depending on which size your plug thread is.

There are 2 bridges with a large square hole in them. I guess that they go over the long thread that would be sticking up out of the head. I guess the bridges sit down on the head studs(?). I reckon that you then put the washer & nut onto the long studs, & wind the nut down onto the top of the bridge; & that then pulls the head up enough to get under it, & get it off.
The bridges are stamped HERBRAND 2390.
My question is, would anyone out there have a copy of any original instructions for the tool, or an old catalogue picture / advert for it?
Or, a picture of a complete set; or even any information at all. What date / era would it be? Am I missing any parts for it?

It'd be great to have some information or thoughts on it, so as I can put it back to use again.

Thanks, Dave.