1. your friends do not know much about big blocks. with the rigth parts they can go to 75000 rpm+ 2. to make a 427 you need a 454 block or a427 block and a366 396 402 427 3.760 crank this will make a 427. some 396 block can be bored out out 4.250 but not all.this wound need to be ultrasonic check for wall thickness.on the heads valve size areO port 2.065 and1.720and gm rec ports 2.190 and 1.880 the O port heads work good and need very little work bowl job and you can put 2.190 and1.880 in them there is the very small o ports and the big O ports look for the big one for hi rpm.and to go to past 6500+ you are going to need some good stuff but can be done i have built many of them