hey guys i'm thinking about replacing some of the speakers in my cab.

its a hartke 4x12, with (im pretty sure) celestion gt-80's in it. It have the impedance selector on the back, with the choice of either mono 4 or 16ohm, or stereo 8ohm inputs. I have owned this cab for 3+ years, after getting for a steal at a closing down sale, the construction is remarkably good for what i was expecting, plenty of bottom end.

i was thinking of replacing 2 of the speakers (probably the top left and right) with some vintage 30's (can't afford 4x vintage 30's)

how would this sound?

and does anyone know somewhere cheap in Aus to buy these speakers? or worth my while shopping internationally (like i end up doing for just about everything guitar related haha). Also for interests sake, if anyone could point me to an Aussie cab maker that is reasonably priced and decent quality i would be very thankful, thinking of simply getting a 2x12 and selling my quad. my back will thank me later

also would there be any issues with the impedance selector?

ESP LTD VIPER 1000 - 18v modded, EMG AfterBurner (replaced tone pot)
Peavey VK100 Head
Hartke 4x12 w/ celestion somethings

ISP Decimator noise gate
Bad Monkey OD