There is an entire document for the Jabiru FWF kit for the 601XL.

I am attaching the version I have, but there may be something more up-to-date on the Jabiru or Zenith sites.

Jabiru_Zenith601-650_Combined_Manual_web.pdf

By the way. I see you are in Virginia. I currently live in Michigan but am building a hangar at Smith Mountain Lake airport (W91) so I can eventually move there. Good to see there is at least one more 601XL in the area.

Love the guys at Arion Aircraft, but providing stuff on their web site is definitely not their strong suit. You usually have to ask.

The FWF kit is  a product of the old Jabiru USA which was purchased by Arion.  The large NACA duct feeds the carb air box

The heater shroud for the carb heat has a single flange, drawing hot air in across the muffler from the ends which are open.

The cabin heat draws outside air from the smaller scoop into the shroud with two flanges.

You mention SCAT tubing - if you have a Bing carburetor one of the things that causes uneven EGTs, etc., is turbulence in the hose between the airbox and carb must be avoided.  The use of a smooth-surfaced tube and an airflow straightener is recommended.  Indeed, I positioned the airbox so as to have a smooth transition between it and the carb. Here is a source of intake tubes: https://www.intakehoses.com/90-degree-elbows.html - Photo one shows my home-made flow straightener.  Photo two shows the hose in place between airbox and carb.  Arion may be able to give you some help with the flow straightener. They've been experimenting with 3-D printing.

I also replaced the bungee suspension with the Zenith Doughnut system while the engine was off.  IMO It would be really difficult to do with the engine in place.