I also have an almost identical saw… It says “Cast Steel” on the back, in the same way yours does… Mine has only 2 rivets though. (Difficult to tell the size of your, but mine has a blade that is 10″)
It was given to me in a pretty poor shape, with lot’s of other “junk”…
But I recut the teeth as per Paul’s method and it really is quite a nice tool now. The handle has been glued a couple of times, but it’s solid.
If your’s is as good a mine, (now), is then you’ve got a bargain for £3!