Speed parts are available for the gmc engines, but they cost more than chebby parts. All the T5 stuff you read for the chebby crosses right over to gmc... only difference is gmc used a pilot bearing and chebby used a pilot bushing. If you are planning to hop up a gmc 6... a 270 or 302 is a better place to start. Gmc engines ran full oil pressure long before chebby motors. Gmc blocks were cast with a higher nickle content so they wear better. Hope this helps