Re: 8.1 litre
GM did a major redesign of the 8100 series big block. According to GM's web site , nearly 90% of the components are different than the Mark IV, V, and VI engines. The cylinder heads are new, with a symmetrical port layout and a revised bolt pattern. The crank uses an integral crank sensor for use with the Port EFI. The latest versions uses "drive by wire" throttle. Becuase of the major changes in the design of this generation big block, I haven't seen any performance parts for it the last a looked, which was nearly a year ago.