malcup - if youve got a Willy 1 that was numbered 416 and had a sunroof its more likely you had some weird cut-n-shut rather than that everyone else doesnt know Willys!
Firstly sunroofs were not even an option on Willy 1 and 2 for the deliberate reason to keep weight down slightly - it might seem silly to save weight through not having a sunroof but thats teh same reason why they didnt have electric mirrors. If yours was a limited edition special then it was a limited edition of one, or it was put in after it left the factory. Or its a Willy 3 which you could tell from the colour which wouldnt be 449 sports blue.
Secondly the Willys did go up way over 400 - in left hand drive only. The first run were RHD for the UK because Frank Williams had #001, therefore the rest of the RHD allocation were numbered directly on from then. #416 would have been a LHD car. Or the only other possibility I can think of, which I dont know for sure about, is that it may have been off a Japanese one. There are Jap Willys but I dont know what numbers they are and it would seem logical that they would be off the first RHD run as well, after the UK ones.
Finally, no-one to my knowledge (which goes back a few years) has EVER come up with number 400 or over as a UK car. Which makes yours decidedly odd. There must be some reason for how you had a 416, but Im damned if I know it.