Good eye, so it's the second iteration of the 400, post THC.Mid to late 60's. Bell keys are on the left not behind like the real 400's. Serial number is probably around 400xxx or higher.
LOL, that's hilarious because I also call that engraving 'bowling ball'...and you are right, same reason, it always reminds me of Brunswick. (never became a very good bowler back then, but I really loved my marbelized teal 12# ball and the bowling shoes....).The floral engraving was used pre-buyout but I think the switch to left sided bell keys happened right around the time of the buyout or just after--'63-'65. Then shortly after that they changed the engraving to the "other" big B. I call it the "Bowling-Alley-Big-B" because that engraving always reminds of the Brunswick bowling logo I remember seeing at the lanes when I was a kid.
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