Mic placement on a 2X10 cabinet

[explodingPSYCH]

I'm gonna be replacing my 1X15 for a 2X10 aviator cabinet pretty soon, and I'm worried I might have difficulties with recording.

I'm used to placing my SM58 halfway between the center of the speaker and the rim, about 6 inches to 1 and 1/2 feet away.

I'm wondering where the best place to put a mic would be. I'd like to stick with the SM58, but I have a Octava MK319 I've used before.

Advice on replicating that simple set up without phase issues?

Thanks,
Johnny