Wow, been a LONG time since I updated this.
Plans changed for the wagon over the course of 2011/2012.
I came across a fresh 508 on CL with a bunch of other parts for a reasonable price so I picked the lot up.
Sold the other parts off and have about 4k into the 508.
I think I did ok, I'm going to blow the bottom end apart and p-gage stuff just to make sure it shouldn't self destruct once it's in and fired up.

While an 8-3/4 would have held up to a mild 383 with a 3rd pedal, a healthy 500" motor would likely break it after a couple beers and friends egging me on.

So, called Cass, broke out the debit card and about 6 weeks later this appeared at the local freight terminal:

Hopefully breaking the rear won't be an issue anymore.

#'s 383/727 is out and in the corner, hoping to have the new motor/trans/rear snugged up under it by spring so it's on the road for good times next year.

Other changes:
Got a decent CD player and some 6x9's in boxes in the back. I don't want to hack up the original interior panels to fit speakers so I'm not quite sure what to do there. I imagine I'll end up cutting holes in the side panels for them since speaker boxes are pretty trashy.
Also, I think the power brake booster took a dump, pedal is very firm and requires significant effort to get the car stopped in short distance. Brakes are good, just seem to lack power. So, while I'm under the dash hanging the clutch pedal assy and changing the steering column I'll replace the booster.