Had a listen last night and even got the girlfriend involved-her hearing is much better than mine.
To our ears the clearest "shift" is indeed at 1:50 although the weight of the piano and change could be considered to be intentional as part of the recording-maybe,maybe not.
Probably not due to the age of the recording.
During the drum solo there are again as described above quite a bit going on,certainly the odd noise which isn't clear (I had to crank the volume up quite a bit to hear what Eileen could hear)-we decided most of these were probably finger noises on the bass or something.
Anyway I certainly never quite noticed that change at 1:50 before as being a tape splice.................