Triumph shows the same filter for the speedmaster and america for the Tbird. Unfortunately, the K&N has a different bottom than the tbird filter and it fits but not very well, and you have to crush the filter a bit when you force it in. Do what i and many others did....get a UNI filter. It is also the same filter as used with the america and speedy and it DOES fit, and perfectly. it is also much cheaper, easier to clean, lasts forever and flows as well as any. I had one in my speedy and now in my Tbird and i assure you they are as good as any. IMO better, but thats subjective. You can get them all day for around $30. I paid $28.
I recently bought a K&N TB-1610 for the T-bird on the K&N website, Ihave not installed yet but I assume they corrected the issue of the fitment because Know they do sell it for the T-bird.