If your seat post clamp or front mech are 31.8mm you can be pretty sure 27.0 will be right. 27.2 is a common size ask around friends/colleagues and try one, if you can only get it in the top inch or so again you will know.
A B17 should have a 30mm seat post, also it should have larger ovation tubing and a longer rear swing arm to achieve the 6" of travel that is unique to the B17. Plus did the B17 ever come with standard disk mounts on the swingarm?
I have heard previously that run out models were painted up without meeting the expected features of the model they represented. Can you measure your rear axle centre to crank bolt centre? I suspect it will be shorter than expected for a B17. If it shorter the good news is a replacement swing arm will be easy to source, bad news is it won't have 6" of travel on the rear.
While the tape measure is out measure the shock length, centre to centre on the eyes, I am betting it will be 184mm.