Sen. Grassley is already listed as the Senate Finance Chairman. He is expected to chair Judiciary after his term limit as Chairman of Finance is up in four years.
Sen. Grassley's credentials as a conservative cannot be challenged.
http://finance.senate.gov/
http://www.insightmag.com/news/2002/11/12/Politics/Iowas.Main.Street.Republican-308296.shtml
Sen. Grassley has more seniority than Specter. I wish he could be convinced to challenge Specter for the Judiciary Chairmanship, but I understand he prefers to remain at Finance.