Looking at your photos, I guess we can rule out the F-13 photo reconn version.
With all the turrets removed, mod side blisters, and the AN/APQ-15 tail-warning radar ball hanging below the twin .50's, it sure looks like a B-29B, except the serial number indicates it being an early Wichita B-29.
Maybe it was a test ship for the APQ-15 or some other project. I don't know of any cross-over serial lists converting B-29's to Bell-Atlanta B-29B's. I assume all B-29B's were new-production.
Heres a link to some more info on B-29B production: http://home.att.net/~jbaugher2/b29_5.html
As far as tracing this frames (42-24512) history you might try the AFHRA archives at Maxwell AFB.
Someone else on this board my have more info as to obtaining service history cards on this B-29.
BTW very nice pix Thanks for sharing.
ref: http://picasaweb.google.com/joepat1947