Mail him the one you used to make the photo?
1972 was it? Nearly fifty years gone, all of that. Lot of it was Bob's "treasure", not mine!
We did that manual on one lone IBM Selectric. White-rubber cemented each page four-up, shot it with a Robertson "darkroom camera" to reduce it to letter-size, small-print.
ISTR I had an OSI Challenger and Bob (K4TJ) had a CPU chip with all of 256 Bytes of RAM.. a "Computer" still said "IBM", UNIVAC", or "Control Data" on the doors. Large doors. Nary a bit of that was "computerized".
All the "original" graphics artwork was done on my drafting table in Inja ink direct to vellum, then shot on 35 mm Microfilm, hand-tray developed for paste-in. "Physical" cut-and-paste. Not electronic. All the while grumbling I had no hot-wax gear as we had at Northrop-Page!
And then? We printed it on cheap sulphite paper. For regular loose-leaf updates.
I had put by ten or a dozen copies when we shut-down the company. They went to mostly brown dust within about ten years!
If I were doing this I'd peruse mcmaster carr for a small spring, like the ones used for drill press quill return. They do have all sorts of
springs like that.
Might not need all that much force? Wire I recall was round, a tad smaller in diameter than the spring in a retractable ballpoint pen. What yah needed, though, was a cavity that allowed for the expansion as the spiral was loaded and the spring changed radius. Also to keep rocks and dog hair from building-up.
A slider that can be remoted inside a nice clean box and operated by a push-pull Kevlar strand is just more predictable as to spring force, Either of a stock compression or extension spring can work. "Both", even, if yah want an assymetrical centering at "hands off", slightly different range and pressure, each end of travel.
Also easier to "customize" as to resistance and
length of "throw" - given yah can wrap the "human hand" end of the Kevlar aound any diameter hub as suits yer need. Or use a lever, more directly.
Not all that different from some of the stuff done in motorcars, actually.
One of mine, the foot-pedal to injector control travels over a data bus.
The other uses a "physical" link. Flexi tube housng carrying a stainless pull-cable, "gas" pedal to underhood TBI.
Person could raid NAPA for those? OTOH, weed-wacker Kevlar is cheap and easy.