The reason they move to the iron block is because its cheaper than the $6000 race block for big displacement without resleeving the cylinders.

The LS1 is plenty strong and is a very stiff cylinder case when compared to the LT1, apples to oranges, both are great engines though. Aluminium is a lot more brittle, but it is very stiff and doesn't distort near as much from heat soak.

 

I don't know if it is cost alone... You could go with Darton sleeves on the aluminum block like the big-cube motors do, but the head bolt seat strength would still be marginal. No one like lifted heads on a FI motor. I'm not saying the LS1 block itself isn't strong, but I think the LT1 bolck is a stronger and cheaper starting point for FI.

 

Use studs not bolts.