Alternator for 620ti- same as 820T

Have seen a vendor selling a Denso Alternator (aircon) for a good price was thinking of buying it for a 'just in case' scenario, problem is the MGR part number quoted is for the 820 Turbo & Rimmers list a different part no. for the 620ti, but vendor states it fits both?

Any knowledge on here?

Thanks.

from the last news http://forums.mg-rover.org/showthread.php?t=730233&goto=newpost

via IFTTT