I've seen that rumor pop up several times, every time someone tries to screw any of it together (Chevy / GMC / Toyota) nothing fits.
Nowhere close.
I forget where but someone had a picture of the three head gaskets laid over each other and IIRC the Chevy is shorter than the Toyota which is shorter than the Jimmy.
As I recall the Toyota cylinders are spaced evenly (IIRC the Chev is in pairs) making for an even more dificult fit (at least for a Toyota Head on a Chev block).
