I don't know about the big block Chevy, but on the SBC you need to put sealant on the inner bolts on the intake manifold.
The inner bolt holes for the intake manifold (in the head) go completely through and are exposed to oil underneath. If you don't use RTV on the bolt threads, the oil will wick up the threads and leak out onto the surface of the intake manifold. However, it should not create a vacuum leak.
For torque measurement I use the torque wrench on bolts I can reach, and then use how tight they are as an estimate for the ones I can't reach. Its not very scientific, but the best I could come up with. Also make sure you look at the suggested tightening sequence so it pulls down evenly.
Bruce