i'd suggest you join the Series 2 Forum (google it) for the correct procedures with your vehicle if it may need inspecting as they are recognised by the DVLA as the authority on 2/2a models and verifying them
i've a 1970 2a that has NO logbook or registration mark that i'll have to have inspected by the club when i decide to get round to repairing/rebuilding it (before i do any work) to get a correct age registration with minimal aggravation
but on saying that...
i think you'll have to mot it for the first time to get tax, then you apply to DVLA to get it's taxation class changed and at the same time apply to get your mot exemption (i could be wrong though)
to be honest i think it would be sensible to get an mot each year anyway, it's always good to have a second pair of eyes look your vehicle over to hopefully spot any problem that you might of missed, it's easier to see under any vehicle when it's up on a four poster than it is crawling around on the floor