While there are billet main caps and block girdles to help get stock blocks to live longer when making more power, 1000+ isn't realistic. For that, the Buick Stage II motors are the ticket. Part of the racing program, they had a bevy of improvements (and beef) to withstand the rigors of NHRA, Indy, Busch, IMSA, and GTP racing. They have thicker webs, four bolt mains, six bolts around every cylinder, etc. The heads are similarly beefier, and have bigger ports as well.
See
http://www.gnttype.org/techarea/pict...lockguide.html for some comparisons between stock blocks and Stage II blocks.
TA Performance is making aluminim Stage II blocks at this time. Plus heads and all the other goodies to go with it. See
http://www.taperformance.com/