FMJ caliper interchange questions

I was at the auto parts store today. Got into a conversation about A body’s. The guy tells me that FMJ spindles fit. Which I know. I’m at the crossroads of calipers now. Sadly these aren’t $12 like they used to be. Anyway, I don’t have cores so I’m paying the full boat retail sadly. Anyway here are my questions.
1- can the spindle be used on either side ? Does it matter?
2- what caliper do I want so I can run in the rear for ARB clearance up front ?
He said Vans of some years fit that spindle. I was unaware of that and am not sure about it. Thanks guys.