The Van's firewall forward kit was very complete. I have the original IO-390 engine and stock exhaust and my plane is a taildragger. But presumably anything that is in the plans will be in the kit. I think I ended up ordering a plug for the fuel spider and a set of hoses from Aircraft Specialty to work with my Half Raven oil separator.
I suggest that you use a 1" 6-point socket to remove the oil filter from the engine and reinstall it yourself before you mount the engine on the plane. I got to my first oil change and had a very frustrating time getting the oil filter off. I think Lycoming had subcontracted Jiffy Lube to put it on. The 1" hex head rounded off, a screwdriver pounded through the filter broke off in the filter without budging it, etc. I ended up mangling it with a giant channel lock pliers. Even if I had to mangle the filter before installing the engine, at least I would have had better access and no oil in it at that time.