They've placed the engine room exactly where Mr. Jefferies original Phase II diagram (as extrapolated by Shaw
) suggests it should be.
I'm really not aware that that is where Matt Jefferies suggested it to be.
On the contrary I'm rather confident that the vertical shaft connecting engineering and saucer hull had been considered by MJ to be a power line (and not a turbo shaft) as early as the TOS schematic in the bridge alcove.
There's also a Phase II pre-production sketch (where did I misplace that?
) that clearly shows the "Mike Minor" reaction pods in the bow of the engineering hull and hints the vertical intermix chamber coil we'd come to see in TMP.
I did contact Andrew Probert on the issue. He wrote me back that the vertical intermix shaft was already there we he joined the production. He couldn't say whether this had been a Mike Minor or Matt Jefferies idea but given the match with the supposed "turbo shaft" I think it was really MJ who put it there.