I will pipe in here and see if I can answer the question .The concern is not so much the guides being to tall it's the seal that get smashed by the spring retainer .I have done some dyno testing with a 300 Hp Flat tappet cam and the engine will make around 325 hp/345 ft lbs torque .Keep the cam small and you will be happy with the idle and power,the vortec heads flow very well .If you would like more specifics on the cam I used PM me I can send you the details I dont have them here at home


In the works 2006 GEN III 6.0 /4L80E/ 205 New process,A/C and power brakes .