I'm looking to replace some factory speakers in my 1997 Chevy S-10
Blazer. I know the dimensions of the speakers a

Dash: 4"x6"
Front Door: 6-1/2"
Rear Door: 6-1/2"

However, if I even HAVE dash speakers, they don't work. The S-10
pickup has the same "front-end" as the Blazer, so I'm thinking that
the dash speakers are only used in a pickup configuration. In that
case, the dash speakers are the fronts, and the front door speakers
become the rears. As I have four doors, I only use the front door and
rear door speakers, and not the dash.

If I were to put some 4x6s in the dash, would my stock POS radio be
able to support 6 speakers? Would a NEW radio be able to support 6?
Lastly, what do I buy if I can't find 6-1/2" circles?

Thanks in advance!