Ok,
Your image seems to show a stub axle that uses a 108? mm CV
joint but the six bolts seem to be M8. Is that the case? Measure
the ID inside the raised lip on the stub axle.
If the bolt circle of your CV joints is the same as your 915 flange,
you might be able to install inserts (casesavers?) in the 915
flange to accept M8 threads.
If your CV joint is 6-bolt 100 mm then it seems like the only issue
is to find the correct 100 mm transmission axle flange
with “course” 18 splines. The critical questions are: Does your
CV joints use six M8 bolts? Is the CV joint outside diameter 100 mm?
If so, you want a flange with a 923 part number. That would
have originated with the ’76 912E but also used on ’77-’83
911s. It cannot be from a 930 or M491.
I think (but may be wrong) that the change from 18 splines to
43 splines happened with the ’83 model 911.
Here are three:
On the left are 108 mm, on the right 100 mm. The 43 spline are
at top, 18 spline at bottom. Of course the one you need? would
be lower right. The one you have is lower left (108 mm CV, four
M10 bolts and two 10 mm roll pins – the flange measures 109.5
mm OD).
It may be a 951 part is most suitable. I’ll try and find out tomorrow.
Best,
Grady