The RV-4 has had only one spar design for its entire life as far as I know. The only "options" where whether one tapered the laminated stiffeners in length.
The spar (similar to all RVs) has a large U Shaped channel (web) that is formed from bent aluminum. To both the front and aft sides of this piece 1/8" thick (going from memory here) stiffeners are riveted to the spar web using 3/16" rivets. The stiffeners strips are about 1 - 1.5" wide and are stacked on top of one another to make the complete thickness of the spar.
Since loads lessen the farther toward the wingtip you go the need for stiffeners to meet the designed load carrying ability decreases, hence the number of stiffeners decreases. Indeed for the last foot or two only one stiffener thickness (forward side) is needed.
Also, the stiffeners were made from 1/8" x 1.5" (I think) bar stock (a standard size. In order to save weight the builder could optionally taper the spar strips in width per the plans. Builders of later model RVs will see the same design feature in the machined dimensions of the one piece stiffener used in later models. Access to a CNC machine makes fabrication simpler than when you are doing things with a hacksaw.
Back in the day there used to be discussions and such in the early editions of the RVator as to techniques the builder without access to a machine shop could use to cut such tapers. The best answers usually involved a bandsaw but using a hollow-ground planer blade on a table saw produced the nicest finish IIRC.
All eventually came to naught as the availability of pre-made spars with machined cut tapers, anodized finished parts, and precise set rivets (in a brake press probably) made user fabricated spars as rare as humble tail-dragger pilots.
So, if that plane is an RV-4 it has a metal spar. Only question is was it pre-made by Phlogiston (a good thing) or made by the builder (something that just needs a bit more inspection but, in itself, no reason to run for the hills).
If, upon inspection you see anything that looks like wood, congratulate yourself on finding a rare, probably one-of-a-kind example of the homebuilt aircraft world. But just know that it ain't an RV-4 even if you can understand why someone might want to claim to be one of the best flying airplanes ever designed.
