We want to thank Norman C. Miller, Conservator of the International Registry of Sunbeam Tigers from which we quote the following information.
There are, of course, many subtle elements embodied in the history of any automobile. Leading the list is the misnomer - "MKIA". While a bit of a mystery, the origin and use of this term seems little more than a convenient method of separating the 1965 and 1966 model years. Most Tiger owners understand it to mean any B3820##### vehicle. The "factory" however, makes no such distinction. There are only MK Is and MK IIs.
Similarly, the persistent rumor of late 1966 Tigers supplied with 289 CID engines from the "factory" is simply not supported by the surviving production records. The engine numbering system used by Rootes clearly specifies a unique alphanumeric identifier for 289s and no entry for a regular production B3820##### car lists anything but a 260. As an additional parallel, we have the ongoing confusion concerning the number of MK IIs produced. For unknown reasons, there were no assigned MK II chassis numbers from B382100003 through B382100099. B382100001 and B382100002 were assembled as production analysis vehicles, followed by regular production continuing with chassis number B382100100.