Ah, the OP is still here...."stupid" 
Merry Christmas. And, no offense taken, I was told where the distib was before "looking" into this more. I couldn't believe it either.
It'll be a learning experience. And, it's gonna cost the owner LOTS in use of his garage more than just storage for a car.
This just keeps getting better:
"routing the new plug wires in the stock looms is, however, a bit of a nightmare.. "
Might I suggest to butt the ends of the plugs together, new to old, and tape them together. Then just pull them through the insane routing that GM chose for this engine.
In reply to Appleseed: Yes, indeed you may, as I was thinking about what to lube them with to pull them through. I'm thinking a little spray dry lube or a dab of white lithium grease. Don't really want to use WD-40,
The designer had to be an ex-Porsche Carrera flat 4-cam engine designer--the air cooled one from the fifties.... I do admire the packaging, but, there was no thought to replacing parts that wouldn't make the dealer a bundle. All day for a rotor, cap, wires and plugs? The Porsche would be easier--even dialing in those gear driven cams...
Off-idle stumbles (particularly if you have the slightly rough running at 1% throttle instead of a bigger stumble at 5-20% throttle is often caused by a dirty TB or a failing EGR valve. I had my EGR replaced as part of the campaign from GM, I still had the teeny rough idle at 1% throttle. I replaced my Opti when the rotor fell off (along with plugs and wires) and still had the same roughness. Had to replace the MAF - same thing. One day when I had the TB off I decided to clean out the gunk - bingo, problem solved.
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