Picked up what I believe is a 1995 Klein Quantum in unused condition. Seller said it started life as a frame that was built up in the shop where he worked and sat unsold for years. It was eventually transferred to the basement to sit. It is covered in dust but basically NOS ~1995 Klein.
What to do with a bike like this?

Ride it! My Quantum II was a fast but comfortable ride. Go enjoy that beast!

1995 Quantum came with RX100 STI - looks legit and ready to ride.

People like these for criteriums, but my Quantum Pro is the best climbing and descending bike I've ever had... I like stiff.

Unlikely that the shop put a wired computer on a bike they hadn't sold - also the Look pedals would've been by request.

one of the best bikes ever built, upgrade it with Dura Ace 7700/7800 and a pair of carbon wheels and you will have a light weight bike

That year of Quantum is going to have the press fit square taper bottom bracket. If you were not OK with the current RX 100 double cranks then you have fewer options for other cranks. You could seek out any 110bcd square taper cranks in order to get a lower gear range for improved hill climbing. You might even get away with running a triple square taper crank with 110/74 bcd such as a deore xt from that era or an XTR M900.

I know how to remove the BB spindle and bearings but I don't possess an original Klein tool nor do I have an improvised tool that can press in a replacement bottom bracket.

If the tires and tubes aren't <5 years old, I'd replace them first (rubber degrades slowly when exposed to air). And I'd also repack the headset and wheel bearings and give everything else a good gentile cleaning and lube as required.

After that - oh hell yes. Go ride it!

I has 2 aluminum Quantums, wish they had lasted. Had top tube sweat corrosion on the brake housing brackets, Klein replaced that frame in '95. The 2nd had its seat post clamp crack in 2000. Could not replace. I would still be using that last bike otherwise, it fit well, climbed great, was comfortable, loved that bike.

I'd ride this one for sure,

Oh yeah, I forgot that the old Kleins used the press fit bottom bracket.

According to the seller, the shop built it up with whatever was lying around. Most of the components are RX100, the handlebars and seatpost are Trek branded, Syncros stem and Ultegra hubs laced up with Matrix rims. I assume that the computer, bottle cage and pedals were thrown on as “display” items but that is just speculation. None of it appears to have been used either way.

Dust it off, lube and renew where necessary, then ride the heck out of it! Great find! Those bikes were hot BITD.

I thought of a joke about this but it wasn't kosher.

Nice.

Like Robert A. Heinlein once said about Jerry Pournelle (both sadly now deceased): I am also a "terribul spellur" (or maybe it was "terribul spellar").

Not sure that "spell-check" qualifies as the best thing since sliced bread, but for me it's close. Unfortunately, it doesn't catch those misspellings that also happen to be correctly spelled other words.

The late Sheldon Brown's BB database says the shell is 68mm wide and 35mm - which is just a hair under 1.378" - diameter (presumably that's the ID). Gotta wonder if one of the current threadless repair bottom brackets would fit. Last time I checked, they're still made by Sunrace and at least one other manufacturer specifically for use with frames having stripped BB threads. (Velo Orange formerly sold one also, but they seem to have discontinued theirs.)

They're unfortunately square taper/68mm only, and spindle lengths are limited. But that certainly beats not being able to ride because the BB is shot.

If so, that might provide a replacement option if/when the original BB fails.

I've never owned a Klein, so I haven't ever had to replace or service a Klein press-fit BB. Anyone out there know whether the threadless repair BB option will work on a Klein frame?

Brilliant!!!

Great time capsule find, also a big fan of these.

I thought I'd just pass over that remark

As the sheep said to the shepherd: "That was pretty b-a-a-a-a-a-a-d!"