Tdub,
You ain't alone.
My '89 B2200 p/u has two cats as well.
I've thought about drilling a hole straight through both cats, to gain some performance (I've got a press and bits up to 1 3/32").
I like your header idea better, though.
I once faced the dilemma that Doc Sharptail just wrote about.
In my case, the pipe and muffler had rotted from the cat, back (typical).
I priced all the stock pieces and found the total cost for replacement was going to be $110 (1993 price).
As Sheriff Bob said in the movie Used Cars, "
That's too high!", so the ol' brain got to workin'.
Turns out the intermediate pipe was only $25, so I took that.
I then found out they had "California Turbo" mufflers on sale...$12.00!
I finished her off with an elbow and a short extension that featured a 45 degree cut, turned slightly so as to miss the spare tire.
Grand total for my home-made "cat back" system?...$50.00
Not sure if I picked up any real performance advantage, but it worked and it wasn't
too loud, so I was happy.
That lasted until about 5 or 6 years ago, when it finally wore out.
I replaced it with the stock system, now $150.00 =(
...but what a difference! For about a day, my truck purred like a Rolls.
Dean