Sonic Flyer, who made this one

[Oilit]

I was looking at the pictures of this bike again and I'm wondering if I'm just seeing something or is there a very weak stamp of a letter or something to the left and up a bit from the first number?
View attachment 1295714

Could be a clue as to when it was built based onninfomin the preceding posts.

I believe AMF at this time was using a system where the first letter gave the year, unfortunately the letter on yours is very hard to see, but if you check Phil Marshall's chart, "H" was 1958, "J" was 1959, "K" was 1960 and so on. If you can't read the letter then matching it to other examples with known dates is your best bet. From what I can see, you're right, early '60's, I think 1959 was the first year for that tank.

 

[Rivnut]

I've only found a couple of pictures of the tank sitting on top of the bars rather than between them.