Your sweet plywood intake reminded me...
I'm just throwi'n this out there as food for "you know what"...
I haven't looked at my stock intake plenum in years, but remember the top & bottom halves come apart...
Would it be possible to utilize the bottom half of the stock intake, to connect to the intake ports on the heads, & fabricate/machine a flat plate to seal the top, that the S/C would be attached to? I was thinking 1/2" aluminium plate.
Like i said, it's been years, so I've probably overlooked a detail or two, but I always thought that this might be an improvement over the cast iron intake lump that I originally received from Alpine.