I tried to download the manual to do the work myself, but it didn't take (probably a problem on my end). But I am very curious, convential wisdom says the 4a begat the TR250, which was a 4a with the TR6 motor and racing stripes. The TR250 begat the TR6, which was a TR250 with a new body. You'd think the frames would be the same with the exception of some mounting points, but curious if the same dimensions are published for both.