How do I know if I can put an Apo Ronar in a #1 compur ?

Hello,

I've seen a not-too-expensive 300/f:9 Apo-Ronar but it is in a barrel.

How could I identify if it would fit in a #1 Compur I happen to own ? SKGrimes reports there are several types, so I'd like to avoid buying the wonrg one.

Thanks in advance

Im not sure if you can short of having someone spin out the cells and measure their diameter. I have one of the wrong ones!