the chassis number in your logbook/v5 and screwed to the bulkhead mean nothing where the model of landrover you have is concerned
just going on external appearances i'd initially assume that it is a S3, S3 bulkhead, screen and wings being the obvious signs, now these could have been replacements due to rot and damage as it's not impossible to mix and match parts between the S2/2a and S3 although the wiring harness and switches generally only fit one or the other bulkhead
so where do we look to get a better idea ??
we start crawling underneath the bodywork and check out the chassis design differences along with the axles and engine/gearbox numbers to see if any of those match it's registered age/model
again a complication can arise from the early/mid seventies when if the vehicle was accident damaged and a determined person could have rebuilt it onto a new factory chassis which would have been a S3 chassis so there would then have been the loss of tell tale design differences, axles could have suffered damage/rot and so got swapped (it's really easy to lose the original parts)
the accurate description (IMO) of this vehicle, is that it's a Bitsa that no-one should get too worked up about, don't go try digging into it too far and accept it for what it is, "just" another 88" landrover that does it's job
i've a Bitsa that i've been driving and replacing/repairing parts on for the last five years, in my ownership i've replaced both dumbirons, welded up a crack in the chassis, changed the engine (that was originally a replacement), fitted three gearboxes, changed the front axle (so wrong serial number on that), changed both diffs (did you know diffs have thier year stamped on them ?? ) and finally changed the springs for parabolics, the chassis number counts for nothing in identifying it now
anyone that wants a "genuine" detail correct S2/2a needs to do thier homework before buying (hinges on doors is not homework), even the rivets to assemble the tub are different between an original S2/2a and a S3
i knew absolutely nothing 5 or so years ago about old landrovers and i'm far from being an expert now, it's just that i've slowly learnt odds and ends whilst i've been tinkering and spending time with folks that do know more than me, plus i do have two genuine 2a's along with my Bitsa