XE282S in my 408??? Big enough or bigger?

That's a real good cam for a mild to moderate 408 IMO... The Racer Brown I have in my 408 is just a little smaller and it works great. I'd also use 1.6 rockers like rumble mentioned. Using 1.6 ratio rockers gets you back the lift loss that is due to the compound lifter to pushrod angle on a small block mopar. If you run 1.5 rockers figure your lift will only be about .500/.520"..

BTW: when you say you have a 3800 stall was that behind your 340 or a 3800 built for your 408? I ask because the 408 will have a bunch more torque. My old engine was a 360 that was farily mild and I had a converter spec'd to stall 3000 with it and that's exactly what it stalled with the 360. I installed a 408 last year using the same converter and it stalls 3500-3600 behind the 408. Huge difference in how it acts. If yours stalled 3800 behind a 340 it'll probably stall 4200-4400 behind a 408. That's more than you'd need for the 282XE cam IMO.

I doubt you'd need more gear with that cam unless you switch to 30" tires. I'm running 3.55's with 28" tires and even with drag radials I'm having a heck of a time getting it to hook up.