I am new here and have now idea how to enclose a picture but I took a second look. The 7 in the engine number looks like a 1 indeed. In the frame is clearly a 1. What does the "7" look like?
Bart I think it would be an impossible coincidence that the numbers factory match apart from that 1 and 7. email me the pictures if you want and I'll post them up for you. Ron
Frame number TL 31649 looks good,same style as this frame number in the photo below.
Engine numbers below are from the same contract as your engine 3HW 41649.
Engine number below is a very early 3HW (RAF contract?) and shows the number 7 stamp that they used.