theres also the option of getting a sidedraft manifold, getting a piece of pipe and modifying it so it bolts to the manifold.
Then you clos eone end of the pipe and whammey, a cheap and easy plenum.
The picture of the one you posted:



looks good. Standard exhaust manifold looks interesting, possibly a jpipe or modified.
Wouldnt be very hard to make the above plenum, the hard/tedious part is making the flange for the head.
I say just go for it and see what you come up with. Should work well