I don't think a thicker gasket is going to help. The height difference in the ports is significant. In this pic I took the big (7777) LT1 gasket and held it up to my LT4 heads. You can get a pretty good idea of the difference.
The Victor Manifolds from Edelbrock have enough meat to allow the porting to get them to match as does the dual plane Performer RPM.
Here is a view of my engine I'm tearing down to give you a little perspective. This is the big LT4 gasket. Notice the difference?
Are you going to drill the intake or drill and tap the LT4 heads? I prefer the head method. You're going to need some tapered washer like these to get your bolts to sit flat. The angles for the undrilled holes are different.
Other than that you seem to have the build figured out. Most Beehives are limited to .600 lift and the 123 Voodoo cam (I really like it) will be a little over that with 1.6 rockers. Lunati lists those cams at 1.5. I know the Beehives won't last very long with a high lift cam like that. Just ask me how I know.
You may want to consider a set of dual springs and I've had great success with the Patriot Gold Extreme springs set up at 1.8" installed height. Plenty of seat pressure and around 400#'s open. I personally think that dual springs are safer also. If a Beehive breaks you're done. Valve for sure and maybe an engine too. Many times a dual spring will just start bouncing around causing really bad float but your engine will live if you shut it down right now..
The Lunati 60122 can easily hit 500 HP and still have a usable bottom end. I know you said primarily track but the 60122 will be great for any street driving that you do and a lot easier on your valve train. Both are superior to the Comp XFI 280 or the XFI 292. I have made 500 HP with the 280 Comp but I have never tried the 292.
This whole post is based on what I've seen and done. Not what I heard from somebody.
Good luck on your build and you really sound like you've got a plan.