Thanks Evan!
Another update - spent part of yesterday digging around on the suspension, and could not find anything that seemed to be loose. However, the right lower ball joint had been replaced with a serviceable one at some point, but I did not see any grease on the fitting at all. The upper ball joints look a little rough, but still seem secure. I greased the ball joint, just in case.
I had the wheels off two at a time, and since they had a lot of brake dust on them, I went ahead and washed and waxed them. That should make it a lot easier to keep them clean later.
I also swapped the instrument panel back out for the correct one. It now has an "idiot gauge" for the oil pressure, but it's better than having the earlier gauge, as it just showed 0 all the time. From my understanding, it needs to have the earlier sender swapped in, too.
Finally, while the back wheels were off, I adjusted the parking brake, so it now works properly. One of them was way loose, and I am wondering if some of the noise I heard under deceleration sometimes could have been the brake pad rattling.
I didn't have time to take it out for a spin yesterday, so hopped in and went this morning. Two miles out, I went to change from 3rd to 4th, and the car wouldn't shift. Coasted it into a dive bar's parking lot, and called AAA. After about an hour, got it home. I had been assuming the clutch slave cylinder went out, but upon further inspection, the hydraulic hose has sprung a leak. I have ordered the part (along with ball joints, just in case), but they may not be here for a bit, which is not good. It eats into what little budget I have, and makes the odds of the car breaking the budget higher if it needs the suspension work. I may need to sell the spare wheels at a giveaway price just to keep under budget, and have to hope nothing else goes wrong.
Current budget without the new parts on their way is: $1975.75, so $31.25 left. I think the hose will take around $14-15, after shipping costs are divvied up. I have the spare set of wheels and the style bar up for sale, but no bites yet. I may need to dig through the stuff in the trunk and see if there is anything that is an easy, quick sell, but I don't think there is.