on 68+ D port heads:
Longest bolts & 1 or 2 studded bolts are right under 3 3/4" long under the head of the bolt or studded bolt, there are 6 of these. Each goes outside the valve cover area above each exhaust port. Above #1
cylinder exhaust port, there will always be a studded long bolt, this is for the ground cable. The other studded long bolt, if there is one for '68 non AC built engines, goes above the center exhaust port (cylinders 6-4) on the passenger side. This studded bolt may not be used on a '68 factory non AC car with Dport engine. By '71 all D port engines received the long studded bolt in this location.
Next longest bolt length, there are three under each valve cover starting with the exact center hole, that makes 6 of this length.
Next you will have 4 (total) studded relatively short studded bolts that are in a low spot on either side of the center bolt under the valve cover area, these are studded to accept the valve cover drippers that bolt under each valve cover.
Next you will have 4 (total) bolts that set down in the very ends of the cylinder head under the valve cover area.
Last, you will have 2 short studded bolts and 2 same length nead bolts. the short studded bolts go on the driver side head, outside down low somewhat recessed on either side of the center ex port area. The stamped steel preheated shroud used from '68-81 attaches by means of these two short studded head bolts. The other 2 same length short head bolts go in the same spots down low on the passenger side outer head.
For those with factory round port engines, '68 1/2-74, the first long bolts & studded bolts mention above, instead of 3 3/4" under the head, measure 4" under the head.