[2.7RACER]

When the cam timing fails to drop into the mid point of the specified range, Simply pull the pin, slip the sprocket off the cam and rotate the cam sprocket 5 teeth in either direction.
This will re-index the sprocket and allow it be pinned in the center of the specified range.
Setting up cam timing to the retarded end or just outside of the retarded end of the cam timing spec's may work ok, but it isn't correct.
Further as the timing chain wears, the cam timing will be further retarded from the initial setting.
For this reason I set my cams slightly towards the advanced position of the cam timing specifications.
I don't see how '75 cams will slip. The semi-sprocket is keyed to the cam shaft. It should be a snug fit.
The pin through the cam sprocket into the semi-sprocket has very small, almost negligable tolerance.
Tightening the 46mm nut will move the timing very slightly, almost negligable.
Of course, a combination of worn woodruff key, in a worn semi-sprocket, with an under size or worn pin, and of course a worn out timing chain, may show the symptoms you have described.
Try rotating the cam sprocket 5 teeth. You'll find it is now possible to time the cam at the mid point of the specification. A few teeth more or less will get you exactly where you want to be.
10 teeth will put the cam back where you began.
This has been covered in the past. Maybe a year or more ago.
Good luck,