It's the same thing as a standard Quantar, they were just some of the last units sold. Same deal with the "MSF Limited" - Same exact radio.
I think the deal with the "Limited" stations was that while they were full-on stations, Motorola wouldn't sell you any options for them after-the-fact. Once you bought it, that was it. I could be (and likely am) wrong.
There are three issues - can the thing do P25, can it be upgraded to the latest software, and could the SCM be modified to non-limited operation. While the SCM hardware is pretty standard each SCM version is defined by a set of resistor links located on the board itself. Within the constraints of memory, etc, you can change one type of SCM into another in a few minutes with a soldering iron.
I understand that the Limited Quantar shipped with the CLN7462 SCM which was replaced by CLN1609 and that the point of the Limited station was to support budget constrained analog systems only. Neither board is listed in my service manual so I don't know what the memory configurations are. It would pay to check this (RSS > Metering screen > SCM) or pull the board and see if it has a FLASH SIMM.
Without the SIMM upgrades will be a bit harder. Without the schematic for the SCM, modification to non-limited version of the SCM will be very difficult.
I guess if you could run the RSS/CSS then you know immediately what was possible.
CLN7462 is the limited board but it has the valuable SIMM, check it has 4 x 29C040 chips on it.
CLN7558 is the EPIC III - nice but the SIMM is not compatible with other units.
CLN6961 is EPIC II - this is my 'go to' SCM never had an issue with these, check the SIMM has 4 x 29C040 chips.
If it were me I'd take the EPIC III but if you want to get just get the thing on the air take the CLN6961 and Flash it up with what's here. Any of the boards will work in any of the chassies. The gold passiviated chassies are distinctly newer than the silver ones but there is no practical difference.
Every Quantar has to be aligned when put into service unless the new freqs are just a few MHz away from where it was last set up. They are not tuned to cover complete bands and that's often why people say this SCM is 'bad' and this one is 'good'.