Aside from having to roll-your-own FWF (with the mount and cowl being the hardest parts), the weight difference between a Cont 550 vs Lyc 540 is significant. Depending on accessories, the 550 could be 50-80 pounds more, albeit with more horsepower.
If you're into doing the engine yourself, which it sounds like, you might just consider gathering parts and building it yourself. If you go with aftermarket and overhauled parts - sticking with stock parts and not getting too custom, you can get it built fairly quickly. And this will allow you to stick with the Van's design for FWF.
Just FYI, the wait time on Lycoming cylinders by themselves is pretty long right now, but JJ Air Parts actually had Superior cylinders in stock when I talked with them a couple weeks ago.