Peavey Classic 30 w/2x12 Extension Cab

First, thanks for all the helpful info on here relative to speaker design/application. My question is in regard to using my Classic 30 to drive a 2x12 extension cabinet with two 8 ohm speakers wired in series, giving the cabinet a functional 16 ohm load at the input. First, does anyone foresee any difficulties as to driving this 2x12 cab with the combo amp as the "head", and second, any suggestions on speaker mixes would be appreciated. My initial thinking on this is that I want to load the Classic 30 combo itself with an ET65 as a standalone blues, rock, jazz/fusion solution, focusing on a mostly clean but edge of break-up, warm ballsy tone with tight bass response, but want more of a Marshall-type response when plugging into the extension cab, without an "over the top" gain sound. Basically, I'm looking for a good mix of both Fender and Plexi tones.

Any opinions on Retro 30s in the 2x12 for this application? Alternatively - although I can't imagine that a total mix of three different speakers would make much sense - again, I'm open to any suggestions. Thanks in advance for any guidance.