Have you ever seen one? The 500cid Caddy hearse sounds good to me. Many Mopar wagons came with 440s, and if you get one that didn't, the swap is easy. I got a complete steel crank 440 with 906 heads for free on Seattle.Craigslist.org, and most times, they are only $200 to $400 for complete motors. 440Source.com has stroker kits with forged crank, rods, and pistons to get you to 528cid for only $1300, and they are coming out with aluminum heads for $800 a pair. The 440 has many more aftermarket parts at much lower prices than the Caddy, but a stock 500 Caddy has 400hp and 550ft/lbs.
Another thought would a '66-'67 Fairlane wagon with an FE motor. There used to be a red '67 around here with the hood, buckets, console etc. out of a '67 Fairlane GTA added to it. It had a 302 in it but it was still plenty cool. Looked factory. Maybe a built 351-W instead with an AOD?