oldbobcat

Axel Merckx, Eddy's son, has a similar build--all arms and legs. Eddy and I lean in that direction, but not as bad. I'm 5-11.5 with 35" legs and a 75" wingspan. In modern bikes, I've found 57-58 cm fits well if the top tube doesn't go over 57 cm. I have a '80 Masi, 60 cm with a 57 cm top tube, that fits me perfectly. With the seat clamp reversed it looks like your upper body position is quite vertical and your leg extension is a little short. I'd venture to say you could get more leg extension by moving the saddle back. You might also get more power and better handling with a lower back angle and lowering the stem. Start with the shorter stem, then see if you can use the longer one without crabbing to the front of the saddle as you ride.

One advantage of those old British frames for you is the top tubes on the taller sizes tended to be shorter.

tangerineowl

Came across this frameset for sale today:- https://groups.google.com/g/650b/c/xmkkpO7dQrA

Raleigh Gran Tour steel 531c with 531fork, at seat tube 64cm ctt, with toptube 57cm ctc.
73/73 built by Raleigh Special Lightweights div. 700x35 or so.

oldbobcat

Case in point, a tall British frame with a short top tube. The proportions for the International are more conventional.