Did my 7.25 take a crap?

Ok, so the last time I tried to get the Valiant going I was having some issues. Shifting into Reverse was pretty rough, and the Drive gears felt very sluggish. After looking around a little, I noticed I was missing a return spring on the throttle pressure lever. See here for a little history: http://www.forabodiesonly.com/mopar/showthread.php?t=147097

I wasn't sure if that was the problem. So today I replace the spring, fire her up and now when I shift into gear (R,D,1,2) I get a pretty decent whirring/grinding noise from the rear end. Did it crap out on me? In neutral the slanty revs up fine and there is no noise. The noise is kinda hard to describe: closest thing I can come up with is the noise an over-revved starter makes. Is that clear as mud? When it made the noise, I did not drive it (so as not to do more damage) so I can't say how it drives/sounds at speed.

When it originally was shifting hard into R, I thought about the u-joints since I've had the same problem on previous Dakotas. But I wouldn't think they'd make this horrible racket when the driveshaft wasn't even moving? But I'm not sure. I was running out of daylight.

Anybody have any ideas on what to look for/check?
It's a '68/904/7.25 with the Slant. It's new to me so I don't have much history on it (for example: like how long the PO was driving without the return spring).