Vintage slotted mags..talk to me about offset

[Tuna Joe]

I currently have on my 1969 corvette (Big Mike thread) 3 vintage Ansen slotted mags. I’m missing one mag on the front.
All are 15x10.
Looking on EBay, I notice they always mention offset and I think it means how far off the hub?

I did locate a set of vintage Indy Mag slotted rims but I have no idea what the off set is and frankly, what the ideal offset should be.
The Indys are 15x10 and 15x8
The corvette is flared and I’m trying to figure out what the ideal tire and rim combo would be for a Motion conversion corvette.

Any help would be greatly appreciated.

Joe