Just finished restoring / upgrading a 1991 Yamaha G9 (electric) and have done a bunch of research on registering it as a street legal LSV. Posting what I've learned for others' benefit. I'm in California. I haven't proceeded with any of these yet, and I'll let folks Google for the specific providers since I can't vouch for them.
1) Getting an MSO/MCO for your cart
I think all the major manufacturers have a process to provide a duplicate MCO, even for pretty old carts. For Yamaha specifically, you can call Yamaha Golf Car customer service and they will send you an email with instructions. They want a notarized bill of sale. Not sure what that proves since I can walk into any UPS Store and have my friend John Q. Public notarize a bill of sale with me. But that's what they want, along with $25.
2) Getting a "legit" LSV VIN number and MCO
There are a couple places online set up as LSV manufacturers who will generate a real LSV VIN for your cart. They provide a VIN plate, matching MCO and federal sticker saying the vehicle meets DOT standards for LSVs, etc. It seems a little sketch to me because they have no way to verify that you have actually installed all the DOT-required equipment like seat belts, brake lights, rated windshield, etc. In theory though, this option bypasses the need to get all of that inspected in California. You do still need to do a VIN verification (form REG31) but that form asks the verifier only to check that there's a VIN plate, federal safety sticker and ownership document (MCO or title) and that the VIN matches across all of those. Normally that form is completed by personnel at the DMV, but it can also be done by any peace officer, or at an AAA office -- who might be less likely to ask questions and just stick to the form. With a real LSV VIN, signed REG31 and MCO, my understanding is that you can walk up to the DMV counter and get title, plates and tags.
3) Become a LSV manufacturer
There's another outfit online that will set you up as an LSV manufacturer with USDOT for $899 one-time fee, no ongoing fees. Then you can issue your own real 17-digit VINs and MCOs. Might be worthwhile for a group who all want to do street-legal carts.
4) Arizona
It seems Arizona doesn't really distinguish between golf carts and federally recognized LSVs. You can walk into a 3rd party title service with an MCO for your cart, and they will give you title, plates and tags using the cart's serial number as the VIN. They don't even need to see the cart or do a VIN verification. Street legal up to 25 mph. They will even do it without an MCO using a bonded title, but then you do need to bring the cart with you so they can verify the serial number. YMMV on how well out-of-state plates will fly with law enforcement. Especially with a local address on your drivers license.
1) Getting an MSO/MCO for your cart
I think all the major manufacturers have a process to provide a duplicate MCO, even for pretty old carts. For Yamaha specifically, you can call Yamaha Golf Car customer service and they will send you an email with instructions. They want a notarized bill of sale. Not sure what that proves since I can walk into any UPS Store and have my friend John Q. Public notarize a bill of sale with me. But that's what they want, along with $25.
2) Getting a "legit" LSV VIN number and MCO
There are a couple places online set up as LSV manufacturers who will generate a real LSV VIN for your cart. They provide a VIN plate, matching MCO and federal sticker saying the vehicle meets DOT standards for LSVs, etc. It seems a little sketch to me because they have no way to verify that you have actually installed all the DOT-required equipment like seat belts, brake lights, rated windshield, etc. In theory though, this option bypasses the need to get all of that inspected in California. You do still need to do a VIN verification (form REG31) but that form asks the verifier only to check that there's a VIN plate, federal safety sticker and ownership document (MCO or title) and that the VIN matches across all of those. Normally that form is completed by personnel at the DMV, but it can also be done by any peace officer, or at an AAA office -- who might be less likely to ask questions and just stick to the form. With a real LSV VIN, signed REG31 and MCO, my understanding is that you can walk up to the DMV counter and get title, plates and tags.
3) Become a LSV manufacturer
There's another outfit online that will set you up as an LSV manufacturer with USDOT for $899 one-time fee, no ongoing fees. Then you can issue your own real 17-digit VINs and MCOs. Might be worthwhile for a group who all want to do street-legal carts.
4) Arizona
It seems Arizona doesn't really distinguish between golf carts and federally recognized LSVs. You can walk into a 3rd party title service with an MCO for your cart, and they will give you title, plates and tags using the cart's serial number as the VIN. They don't even need to see the cart or do a VIN verification. Street legal up to 25 mph. They will even do it without an MCO using a bonded title, but then you do need to bring the cart with you so they can verify the serial number. YMMV on how well out-of-state plates will fly with law enforcement. Especially with a local address on your drivers license.