Quick update here:
Thanks Vinnyeh for giving me Dave Loughran’s e-mail. He has helped sort me out.
I tried using the beer can shim and that didn’t work. So, I re-examined and re-measured the seattube and discovered it was ovalized. Even with a shim, I would get fore/aft movement (but not left/right). The seattube measurement was 31.86 left/right but 32.1 front back.
Once we realized the tube was ovalized, Dave arranged to have a replacement frame dispatched to me. They say they are going to measure the replacement to make sure it is to spec before sending it out.
Assuming the new frame arrives in a timely manner and is as described, I will have reached a satisfactory conclusion on this.
As much as this has been a hassle, Dave was very reasonable and timely responded to my e-mails.
Thanks everyone here for their responses and suggestions.
I will report back when the replacement arrives, hopefully with pics of a completed bike at cyclocross practice.
–Cheers