You are certainly not the first to consider putting throttle bodies on the end of the plenums. A friend bought one to do the same on a Griff 500 - but we quickly realised that it was unsuitable and sold it on before getting past the second design round in the pub!
Thor manifold is designed for low end torque that a heavy 4x4 requires, which is why it has long thin runners. From my Rover v8 Manifold archive Jonathan Douglas of JE Engineering commented:
'the throttle body has a 68 mm throttle as standard and again, we often take this out, in this case to 71.5 mm. The Thor manifold, when used with either a standard cam or a mildly tuned cam, gives a strong torque peak at around 2,000 rpm, much higher than that achievable with the Lucas plenum design, but even with careful gas-flow work the power is limited. We find it difficult to achieve more than around 280 bhp with this manifold, where a similar amount of effort on a Lucas Plenum manifold will yield 320 bhp (but with less torque below 3,500 rpm'
Rover manifold archive:
http://www.mez.co.uk/ms12-new.html
