the problems I had with the frames yesterday were down to not putting them together straight to start with (although that was definitely a problem).
This morning I spent quite a while making sure they were nicely aligned both to the footplate and against the wheels before gluing them back together. Once the glue had set, I placed everything back on the rolling rode, and while I got some movement, it wasn't fluid and smooth, but the clearances appeared perfectly fine. On closer inspection I realised that the problem had nothing to do with the clearance between the frames and cranks, this time at least, but that the brake detail on the frames was pressing against one of the rollers which was causing the roller to stick which in turn was stopping the wheel from smoothly turning; in other words it was acting as a brake!
Moving the whole thing off the rolling road and onto the track and it moves nicely. Now I just have to put the coupling rods and bushes back on and hopefully that will be the first part of the motion assembled and working.