eh ? You asked the question and even gave the solution
I regularly fettle and even and fit modern parts to old bike, older than yours.
We are just giving solutions
the wrong style front mech fitted, the solution is to use the correct style or live with the bend in the cable and the increased rub and friction that causes, if form comes before function that is.
(M953 to keep in in style, also as period correct as you get, with the rest as I guess that's probably M952 ?))
Though playing with cable guide position at the bottom bracket might help a bit, try moving it to the none drive side to get the cable straighter,. Some are multiposition and with a conventional style you might be able to get it to guide over the plastic up the centre so it doesn't rub against the frame/welding.
The problem with using cable outer-inner I've found is mud and water will get in and grind and rub and rust and that's the other end of the seattube away from the tyre mud dumping area.
...just trying to help...