[Mr70]

"Does anybody know if 1970 Chevelle convertibles offered the same 4 speaker AM/FM stereo front/rear fader radio as the hardtop? I'm not aware of any special radio model just for convertibles."

That's right Jim,there wasn't any special radio just for the convertibles.
There was however an AM/FM MONO radio(RPO U-69)that looks nearly identical to your STEREO radio,that would show an ID tag of 01AFP1.In conjuction with the single center dash speaker,this radio would have used the single seat rear speaker(RPO U-80),if so ordered,in the back tray of either the hardtop or convertible bodystyle.

There were Five different in dash radios available for the New 1970 vehicles:
RPO U-63 AM Radio (single ft. or rear spkr required)
RPO U-69 AM/FM MONO Radio (single ft. or rear spkr. required)
RPO U-79 AM/FM STEREO Radio (came w/4 spkrs.included)
RPO UM-1 AM 8Tk STEREO Radio (came w/4 spkrs.included)
RPO UM-2 AM/FM 8Tk STEREO Radio (came w/4 spkrs.included)