The Digikey part number that I mentioned does indeed come pre-assembled but it's not quite ready to use as is. Although the 4 sub-C batteries are connected in series (via welded tabs) the V-shaped battery pack contacts need to be removed from the old 82033 and soldered to the tabs at the end of the assembly that you buy from Digikey. This is a pretty simple soldering procedure, but it has to be soldered for a good contact.
Getting the old cells out of the black plastic frame of the 82033 pack is pretty straightforward. You'll need a good, strong knife, I like to use a heavy duty X-acto knife for this. Cut deeply into each seam of the 4 corners and cut along the seams on both small ends of the pack (the seams along the long sides of the pack are not glued together). When you've cut deep enough into these places, insert the knife into one of the corner seams and give it a twist, the pack should come apart -- if not, cut deeper into those same places.
After soldering the V-shaped contacts onto the new batteries, I like to close up the plastic frame with Duco Cement and clamp it until its set. This holds it together well enough and makes it easy to open in the future.
The only potential complication with using the Digikey replacement batteries is that some of the very oldest 82033 packs have the V-shaped contacts attached in the middle of the pack instead of at the ends. If this is the case there are several options: (1) take apart the Digikey pack and reconnect it like the original HP pack, (2) make your own V-shaped contacts that are long enough to reach down from the end of the battery pack, (3) add a wire from the end of the battery pack to the middle to connect with the V-shaped contact. None of this will make any sense unless you have one of these packs, but they are rare, so don’t worry.