BTW, I'm mindful of the fact that you are intending to use an iron block, which is not going to be hydraulic ready. As others have noted, getting
oil to the needle bearings on a roller rocker is a prime consideration in an FE block...so make sure all the tricks are utilized...a bit more
oil pressure, etc., and remember to keep blipping the throttle to create splash.
This is why, IMO, solid rollers tend to have an easier time running down the quarter mile than in stop and go down a highway. It's the idling and slow speeds that kill them.
Are you stuck on an iron block? By the time you get one sleeved and cleaned up, the arruminum blocks end up costing about the same. Just something else to think about.