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Thanks. The photos helped, and I've been able to track down a few dimensions:

Diameter / width of alternator case (not including mounting ears):
1G small: 5.51"
1G large: 6.25"
3G small: 5.20"
3G large: 5.90"

Length / depth (front of mounting spigot to back of case / bearing housing):
1G large and small: 4.90"
3G large and small: 4.50"

Mounting - centre to centre:
1G small and 3G: 6.93"
3G large: 8.11"

Compared to my 1G large case / frame, the 3G small frame alternator is 1.05" smaller in diameter / width, 0.4" shorter and the body of the alternator mounts 0.59" (1/2 of 1.18" difference between mounting ears) closer to the mounting spigot. All of these tighter dimensions will help with my clearance issues. The small 3G is 95 amps and my current 1G LC is rated at 100 amps, but I've also seen charts that show the 3G producing far higher output at idle and lower RPM than 1G, so I don't see any issues there.

Anything I'm missing?

Great info on the above dimensions :wink:. There are 2 different large case 3G alternators using the pivot mount, I use the one on the left that has 7.00" bolt centers, easily fits the stock 460 alternator bracket(on my application anyhow). The 130 amp large case 3G puts out about 80-85 amps at idle(1800-2000 alternator rpms) and about 160 amps at "full tilt", so they do have a built in amperage "headroom". Hope this helps.

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