I assume you are talking about the Rootlieb Speedster kit? I have built more than a few of those.
You can use a 1926-27 frame, but the problem is that the rear crossmember is too long. If you cut the crossmember, it will work. You will also have to cut the "ears" off the 1926-27 front cross member that are part of the fender mount. It would be easier to find a 1925 or earlier frame. They are common, cheap and make for a nicer installation. The rest of the 1926 chassis parts (front end, rear end, springs, engine assembly, etc) will fit onto the 1925 and earlier frame.
Also, if you decide to use Rootlieb's speedster rear crossmember, which will lower the chassis, it works much easier on the 1925 and earlier frame.
Let us know if you have any other questions. Model T speedsters are lots of fun and a great way to experience early motoring. Good luck with your project.