John,
letting the traveler fall off gives a tad more vertical pull on the boom in close reach situations. A simple boom vang would take over this function for broad reach. A mega-boom-vang (20:1) could be used even upwind and make the traveler location less relevant. Many people here swear by this beefy vang (and call the method of sailing with it "vang sheeting").
Mounting two upright blocks at or near where you have the holes and stopper knots today is definitely workable. Phill Root describes such a system and I've copied it. Instead of a horn cleat, I followed his suggestion and mounted a simple hook. I don't know whether your '83 has a rear deck with wood coaming like the older DS1s. Mine does and I've simply screwed the hook into the back side of the coaming. I have a knot with a loop at the mid-point and that knot goes over the hook when I want to lock the traveler.
If you don't' oversize the traveler you can tie both ends to your block, and leave a loop in the middle. I used some spare rope, so mine is oversized and all I could do was a single standard knot around the becket of the traveler block. That left me with the two ends of the traveler and a challenge how to tie them together and yet have a loop. I solved that with a sheet bend tied with one of the ends doubled, which leaves a nice loop sticking out of the knot.
(Imagine you had doubled the red end, then you would have a nice small loop sticking up in this image. The knot will not come apart if pulled that way)
I originally did it that way as well so I could experiment with slightly different lengths of traveler. Now, after many seasons, the knot around the becket is so tight, I cannot undo it any longer
and until it's time to cut apart and throw away the traveler I'm stuck with it the way it is.