Check
www.carlsfordparts.com he has a few NOS 428 service blocks for $2250. I bought one years back (for lots less too) from Carl. Came in the original Ford box with C6AZ-6010-F part number. That's about the only guy I know with NOS FE blocks. Now for used blocks check
www.dscmotorsport.com a good selection of blocks. He has quite a few 428 blocks for sale. Both these guys are great to deal with. G.