Candace,
Are the two vintage needles you have the same in the other dimensions as the current 15x1s? I only ask this because I have 15x1 needles from vintage to modern in many many brands, and so far I haven't' found a machine that won't use all of them if "it"s in good adjustment.
Is it possible someone moved the needle bar a bit and those are not 15x1 needles?
Just asking cos I haven't run into the problem you are having, and I don't have a Bell machine to mess with.
Joe