There's a great movie clip that shows P-51 production at NAs old LAX facility. It shows one guy "mating" wing halves on an assembly line, actually bolting them together. Later in the clip it shows much of the final assembly which looked more like an automotive production. Little production tooling was utilized at this stage of production, it seems all the components that were jig built were completed as large sub assemblies that needed little or no special tooling for assembly. Most WW2 fighters I've seen up close and personal seem to be assembled this way.
Now let's talk big planes (Listen Up Syscom). From your B-17 to B-24 through your B-52 and modern airliners, putting the wings on was done at an assembly "segment" or "station" called "Wingmate," pretty much common through-out the aircraft industry. At that point the wings were joined to the fuselage using tooling that usually set the wing into splice plates that were already installed on the aircraft fuselages. This had to be done with care and precision to ensure things weren't going together crooked. On the B-17 there also was a large fitting that incorporated 2 high strength bolts (upper and lower)
Here's a photo of a B-17 fuselage on a crane, the lower and upper portions of the wing rib profile is where the splice plate would be.
Here a B-17 Right wing (upside down)
Here's the wing mate station, if you look closely you could see the special dollies supporting the wings as they go together....
Once at wing mate dozens of high tolerance holes were drilled through the splice plates for close tolerance "Hi Locs" or "Hi Shear" pins cold be installed. These are close tolerance steel pins that are installed similar to a rivet but they have a threaded stem. A nut is screwed on and when seated an upper portion "snaps" off ensuring proper torque and semi-permanent installation (these could be removed but it could be real tough.)
The complexity of this assembly is ten fold when compared to a single engine fighter. The B-24 employed a similar installation but the wings were first joined to a "Stub Wing" and then assembled to the rest of the fuselage.
Here's a crashed B-24 wing. The blue and red things that look like nuts are hi-loc or hi-shear collars
This one tore away inboard from its splice plane, note the sheared wing spar.
Here's the P-51 wingmate - notice no jigs or platforms needed for this operation.