For your off days I would recommend swimming and/or biking. Why no strength training? It sounds like you have plenty of muscle that just needs to get leaned out a bit and you have a need to increase your stamina.
FWIW, I'm 5'8" as well and now down into the mid 190s, however, I topped out at something over 250 last summer (I stopped weighing myself when I couldn't look in the mirror any longer) so other than the power lifting thing, we have quite a bit in common.
Keep us posted on your progress through the C25K program.
Regards,
Dale