The heads DEFINITELY DO NOT have to be on the block to determine TDC. When #1 is at TDC, # 6 is also. When the crank, camshaft gear and chain are aligned for installation , #6 is actually the next cylinder to fire. Believing the larger of the two valves is the exhaust on a stock Vortec 350 is a mistake. Place ur head on the block or visualize which valve is at the end of the intake runner. There is the intake valve. Simple, it`s the bigger of the two. The pushrod goes straight down from that rocker arm to the intake lifter. From it`s front, rotate the engine clockwise until that intake lifter just begins to rise. Then re-read post #5. Both lifters will be down and on base circle. Do it once and you`ll never forget how. Why are you concerned about TDC? There is no great need at this point unless for a cam replacement or degreeing.

 

I'm concerned about TDC because don't want to screw things up. Now you know there are 1.5 mil mechanics that think they know. You hear so many different ways to do things. I just want to do it right and correctly to keep from going back in there. 4 different mechanics said to make sure your at TDC

 

When #1 cylinder is at TDC, both the intake and exhaust valve should be closed or close to closed. If you took your intake manifold off to remove the head, just look at the lifters and compare them with each other. If they are both low in their bores, your at TDC.