Yesis there anyway to share more of arekas photos? Especially the trapeze setup.
Here's a view that shows the approximate setup and location of the trapezes. This boat has the contemporary "rope/plate" style handles - you grab the rope, and the plate stops your hand from sliding farther down. The plates should be roughly at same level as the top of the boom (lower measurement mark); if you use another style of handle (such as the T- or triangle-shaped ones), they should be about 10 cm higher. The exact position is determined by crew size and his/her personal style and preference.
The rope/wire joint doesn't have to be that high, but it can as it's not very critical. About half of the rope length on this boat would still be fine.
The fairleads or blocks for the return elastic on the side deck should be located like this, distant enough from the chainplates, so the trapeze doesn't get wrapped around the shroud that easily. On many 1970s boats this is a problem (and is rather easy to fix).
A closer look at the wire/rope joint. This can be tied or spliced in any way you want really.
The other types of handle were usually connected directly to the wire (which meant that the wires were longer), but there's nothing that keeps you from using a connecting rope with those, too. The original wires for your boat very likely need to be shortened considerably. (Have you found them yet?)
Here's the handle, height adjustment system and ring. The rope is slid through a piece of plastic tube for better grip (which could be twice that length). The standard choice of cleat is a Clamcleat, but a block with an integrated wedge cleat is fine, too.
The return elastic is attached the right way, so that it releases the ring from the harness hook just by pulling the handle.
On the opposite side, you can see the elastic go behind the blue spinnaker bag...
... to a turning block near the mast step, and continuing aft...
.. to another turning block behind the centreboard case that sends it back forward, to the port side trapeze:
This is a fairly standard system, but there are countless other ways to lead the elastic, including having it crisscross hidden behind the spinnaker bags, or leading it to the transom along the side tanks, etc. The two sides don't need to be connected, but it's a neat way of doubling the stretching length.
Hope this answered some of your questions