The two latest indy block motors I built follow the same trend I've seen for a very long time. The first was a millennium head hemi that made as I recall 1180, while on the dyno power started falling off. Couldn't find a thing wrong, but decided to pull it apart and see. Found 3 cylinders way out of round. Re honed it, and power came right back, for 2 pulls, and back down it went, but not as far as before.

The second was a nitrous motor, that from the looks of it probably made 750-800NA, with a 350 shot in the fogger. When I tore it down to build it some cylinders were so out of round they had galled up the pistons in places. one cylinder was .007 out of round. The worst out of round I've ever seen save an explosion. I re built it as an NA single 4, and made 970. Power was stable when it came off the dyno.

All the indy blocks I've done have been fine at or around 1000, much more, and they've all suffered. That's just my experience with them.