Wow really 300 LBS back then? Then again, the WWWF was a "big man" fed back then.
Yes, if you look at pictures of Mike McCord vs. Austin Idol, he dropped a lot of weight when he became Idol. As far as I know there's only one video of him pre-Austin Idol and it's wrestling as Dennis McCord in Australia. Even in this short clip, you can see that he was really pushed as a powerhouse.