Will the RB26DETT's intake manifold and throttle bodies bolt up to an RB25DET's head?

Not without an adapter plate of some sort which would be custom made. Honestly not worth the hassles when there are after market plenums for the RB25 head. That and if you want serious power binning the 6 throttle body set up on the RB26 is the norm to a single throttle body.

Really, now? I'd have thought the individual throttle bodies would have been better.