I am old school and heel & toe. Wevo coupler & factory short shift kit adjusted well. Rebel motor & trans mounts to keep things in place. Upgrades made a significant shifting improvement. I run an '86 915/72 these days.
A 915 is not a G50 by any means but that is the skill building attraction.
IMHO. If you want it to shift like "butter" then the 100,000 mile wear parts may need matching replacement. Read some of Zimmermann's articles.
UPDATE: Just got my 915/72 (73F) really rebuilt. All dog teeth, all synchro rings, 1/2 slider, 3/4 slider, nuts & snap rings, and Rebel bearing plate. It was not cheap. As a biker once told me "good food ain't cheap and cheap food ain't good".
Some Bozo had "flipped the synchro rings" and ruined the 1/2 & 3/4 sliders. 915 wear parts "break in" to mate with each other. Replacing 1 or 2 parts will work but it will not make you happy with your 915.