If this thread as already been beat into the ground I apologize initially. I have plans to build a 408 iron block. In the mean time, by bank account says that is not going to happen. I plan on upgrading what I have now on a 98 LS1. I plan on heads, cam, and an intake. My question, if eventually I decide on a 408 Iron, will the heads, cam and LSX intake be compatible on that block, or will this plan be a terrible waste of money?

 

The heads and cam will be compatible, however they may not be optimized. Heads and cam that are very big on a 346, may be very small on a 408. The big cubes needs to flow more air and therefore a given size head or cam will act like a smaller one in the big motor. The intake should be fine though, assuming its a 90/90.

 

Your thread title is misleading. The 408 conversion is simply a 6.0L iron block in the LS1 configuration, it's not a question of LS1 to LS2 compatibility...or it shouldn't be. If you do get a GENIV block then you have issues of knock sensor compatibility.

Make sure to get a GenIII iron block and your 408 will be absolutely compatible to the last bolt.

You do want to consider what the previous poster said. If you get heads/cam now, then you will either need a set that's optimized for the current block and sub-optimal on the new one or vice-versa. (or a compromise between the two).

Personally, I'd get the heads intended for the 408 and the cam optimized for those heads with the 346, and budget a new cam with the iron block conversion. That way you are still pretty good with the current motor and then optimized on the new one.