This should help you out a little:
http://67-72chevytrucks.com/vboard/s...75#post1310375
Although - the original poster isn't responding to that thread it doesn't seem...I had a question for him, and he didn't reply.
That is a nationwide company that you should get some pretty good service from.
I have an aftermarket underdash kit that is a lot more compact than that in mine, but it is a local hot rod company that is building up nationwide right now. I can give you more info if you want me too. PM me.