Expert help needed on 915 gearbox identification.

[Luislang]

To my august fellow Pelicanites..
I have two 915 boxes, one older, one newer. I need your help to identify the year/ specs. Neither box has a serial number, but the bell housing casting numbers are: 915.301.101.0R for the older box and 915.301.101.7R for the newer box.
The older looks like it is magnesium with mechanical speedo drive. The newer box is aluminum with electronic speedo pickup. Any info on their provenance?
Thank you in advance for your help!

Secondly, the older box came with the car and has 108 mm dia. axle flanges. The newer box has 100mm flanges. I'd like to use the newer box and want to determine:
1. Are flanges interchangeable? Can I simply swop the flanges? If not, is it possible to fit 100mm CV joints on the original axle shafts?
Thank you again in advance for sharing your expertise!

[group911@aol.co]

Look for casting dates on the parts to determine approx years. It will be numbers in a small circle.
Unless the aluminum trans is a 77 or so, it will have fine spline flanges. If it's coarse spline, you can interchange the flanges. Easy enough to pull one from each and see if they are the same splines

[Walt Fricke]

The last of the cable speedometers was 1976.
The first, at least for US models not counting Turbos, with an Aluminum case was 1978 (unless end of '77 production had some).

[Luislang]

Thank you, gentlemen!
I'll do so disassembly...
Your help is much appreciated