As you guys keep linking my thread I thought I would comment
Steve is correct that the runner lengths are very well matched to the stock cams so this is something I haven't modified. The challenge that has been advertised through multiple vendors and threads. The front two cylinders get starved of air. Plenum spacer will help to an extent but i thought I'd have a go.
On a thread on my350z.com on a stock 276bhp car they put a modified plenum on and gained 5/6bhp. On the rev up cars the runners are alot shorter which looses alot of TQ but gains topend grunt. This is why just bolting on an older design 276 on a 296 without modification would significantly increase midrange TQ. the shaving of the front two cylinders only adds a little, but if it helps its better than not having it in my opinion.
For reference this isn't a scientific experience I shaved from 15.6mm down to 12mm on the front two cylinders and removed the MR1 and MR2 logos out of the lower collectors.
Not sure how much power it gained but I do know Im 274bhp @ the hubs with stock airbox, plenum spacer and exhaust with Uprev tune.