Can I check this is the right steering wheel for a 77 carb BB

I'm not a steering wheel expert, so take this with a grain of salt. That said, I don't think that's a 512 steering wheel. Was that steering wheel already on your car?

It appears to be MOMO (you can see the logo peaking out), but maybe from a different car (308?). In '77, I believe the wheel center on the 512 is more defined, whereas the 308 is more smooth. Attached are two pics that show the difference (both '77).

I believe they're anodized, but yours doesn't look anodized. Looks like it was stripped and recovered (covering some of the MOMO logo). Looks like someone tried to re-brush it as well.

Also (again, not an expert), I thought the rear stamp was the date of manufacture (loosely). Eg, "4 - 77". I don't know what "M 20340" means.

Side note, I believe the later wheels (BBi) went to the smooth wheel centers, with black anodization. Those wheels have a flattened grip (also used on the Testarossa). MOMO sold those under a different name called "Gritti", with clear anodization.

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That's a recovered 308 GTB/S carb steering wheel.

Should be the same as a 365BB, 246 (no holes version), 308 GT4.
https://images.collectingcars.com/069123/Ferrari-512-BB-Collecting-Cars-054.jpg

 

Momo marking in the 70's.