Greetings all! I'm in the process of restoring an '84 Trek 830. It was all original, a little rough, but generally solid. Sorry, I forgot to take a before picture before the disassembly, sanding and priming. Anyway, it has really smooth "Suntour SF sealed bearing hubs". Are these cartridge bearings or traditional cup and cone? They are so smooth and well adjusted I'm a little hesitant to tear them apart!
Second question: The crank is an SR CRC-T300 with an unusual inner chainring bolt. It looks like it's stepped down to a smaller size than a traditional chainring bolt, with an integral spacer on top ~2mm. Two are seized and will have to be replaced so I can replace the inner ring. The LBS just said "those are really old", couldn't help. Does anyone know where to find these old critters, or have any lying around to sell me on the cheap?
So you're asking, "why restore that bike?". From what I can tell it's the technical equivalent to a Trek 520, which is a pretty desirable bike right now. Besides, I'm fascinated with the early mountain bikes before suspension, bar ends, aggressive geometry...index shifting... when it seemed like a cool new way to get out on your bike.

We rarely, if ever, say that.

The 830/850 differed from the 520 series bikes in accommodating smaller diameter, wider (26" x 2.125") tires, and slightly more relaxed front-end geometry.

I have a '85 Trek 870 that I put 700c wheels and 700x35 tires on. To make the brakes work I put a Peugeot cross bike front fork on and V brake, on the rear I made extenders so the pads would hit the rims and a V brake.
I also swapped out the friction shifters for Rapid Fire 7 speeds, with brake levers. I left the gearing stock.
It makes a great foul weather ride with Planet Bike fenders.
I would say, go for it!

Many, many differences between that bike and a Trek 520, they really are not comparable. Kind of like comparing a Chevy Impala to a Chevy Pickup truck.

Nothing wrong with vintage MTBs, they can make a tremendous value. I have several myself, and on my last vacation, when it came time to take just one bike, I took my $40 Univega Alpina Pro. Go figure.

Vintage MTBs get no respect in the marketplace (OK, there are a couple of rare exceptions), even though they would make suitable rides for 75% of the buyers out there.

As far as the bearings, they should just be loose balls. Sealed does not equal cartridge. Sealed tends to refer to the dust cap/shielding.

1. Whether the hub has cartridge or cup and ball bearings, and whether I should tear it down if it feels perfect.

2. If anyone has a source for the described inner chainring bolts.

If you don't know the last time they were done, service the hubs. Check with these guys for bolts.

https://www.loosescrews.com/