Anyone have some success stories for speaker sizes that fit well in the stock holes in a 77?

Looks like there might be depth limitations . I also imagine no speaker lines up as far as bolt pattern , but maybe get lucky. This Reno car I’m doing has a vintage Sansui stereo that I’m  going to try and utilize , but the speakers are shot. Don’t even need anything great , just something that fits. 

I bought some cheapo Pyles from Walmart for behind the headrest. They work pretty good as a midrange speaker, two way only I think.  Need more bass and treble to be "perfect". 

$20 some odd dollars, can't remember if they were 5" or what but they had them on their shelf.