I've got 2 vintage 70's Pressey speaker cabs (with a 12" Pressey and a Pressey tweeter in both). The weren't originally for guitar.

My question is, I've hooked up a Teac AX-75 MKII stereo amp to it, and my guitar straight into the stereo amp's mic in works (and sounds pretty good)... but am I able to put my guitar into my pedal, and then plug my pedals 'out' into the mic in, or will it be too much power and blow the amp or something?

Of course, an Epiphone Valve Junior head (which I want to get) will work fine I suppose (8ohm speakers).

Thanks for any help! I really want to test these speakers with my board.
Yeah, putting pedals into the mic input should be fine. It may start to clip if the level is too high, but you won't actually damage anything.
Yup, it works, my Boss OS-2 sounds a bit ****ty though (probably would sound heaps better with a Epiphone VJ).