The most cost effective way depends upon how much work you can do yourself. I looked long and hard at MMR long blocks and that was before they came with TrickFlow heads. They also come with a warranty.
Their Street Mod 600 is designed to handle up to 600 rwhp. It costs roughly $7,000. For an additional $600 they will install and time aftermarket cams. I doubt you could pay someone to tear down your motor and build it back up for the same cost.
ProCharger P-1SC, 9 psi, STD 396/383; Uncorrected 388/375; SAE 383/370.
Ret. USAF 1969-1973,1980-1996: Vietnam veteran. Aircraft maintenance. R & D, ICBM Operations.
Also own: 1997 Harley FXDWG, 1998 F-150, and 2002 Corvette LS1