How about making billet runners ?
Lets say there could be a runner length and taper that would work good for 540-572 B1 orig. heads that at least 4 or more could use. We could then ask for a price, like a group buy.
I bet there is lots of costs to be saved in programming and fixture for milling these in a 5-axis cnc mill.
I would like to have o-rings and four allen bolts 1/4 or smaller in both ends of the runner.
If you change deck height in a future build, you could use the runners for another engine and build a new plenum.
My budget will not allow for this build, this winter, but probably next winter.

Here´s an example I found google the net, but with very short runner length.
http://www.williamsenginedesign.com/_/rs...8&width=428

Tom