Your dropbox links did work. I am not a Jaguar person so I can't suggest which model(s) they might fit, and there are not many good pictures of the 420 on-line.
I did find a picture of a front
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it doesn't look as though the depressed area in the middle is in my picture and the taper on the extreme ends doesn't look the same, but the position of the overrider holes does look about right.
Pictures of the rear are even harder to find but I did find this picture
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it looks at though the overrider holes are in the right place for a Jaguar but the angle on the bend doesn't look quite right.
My conclusion is that they are almost certainly Jaguar, but they might not be the 420. Can the person you bought the job lot from tell you what model they came from?
My suggestion is to put them on ebay as two separate listings because you can't be sure that the front and back fit the same model. If you list them as part of a job lot advertised as Jaguar parts, which you bought because of the parts that you needed to restore your own classic and you are selling on the parts that are no use to you but are in very good condition. Admit that you don't know exactly which model the part is for and ask bidders to be sure they want to buy it before making an offer because you will not accept returns.
I would be inclined to put measurements on the photos too, so that potential buyers can compare them with their own bumpers, which will give them less excuse to argue they bought in good faith.
Good luck - and be free to ignore this suggestion if someone else replies with a better one.
He said he inherited it all when he took over a rented lock up garage and that it was all there, along with a load of other stuff when he moved in.
He managed to correctly identify a pair of Mark 2 bumpers, because they are both quite distinctive, so advertised it as a lot "including Mk 2 bumpers" - He insisted that he was not going to split the lot, so effectively passed the problem on to me
Thats probably what I will end up doing, although I am going to try a couple of the forums / owners clubs first.
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