1) 350 Pontiacs ARE VERY different from 350 Chevys. As you found out, all Ponitac blocks are the same external dimensions.
2) You have a Pontiac engine if there is an "air space" under the intake manifold. That's the fastest way for a novice to tell.
3) A 400 block from 1968 is the same as one from 1973 except the locations of motor mount bolt holes. This is a long discussion. Internals are all the same. The water pump and timing cover can be different.
5) Two letter code stamped on the front of the passsenger side cylinder bank, along with the four-character date code next to the distributor hole define the size and factory rating of the motor. The date code is a letter followed by three numbers. The last number corresponds to the year, i.e 9 is 1969 or 1979.
6) Aftermarket manufactures don't have a whole lot of Ponitac stuff unless you kow where to look for it. Summit, Jegs and P.A.W. carry a lot of aftermarket Pontiac goodies.
7) Replace your waterpump with a high volume "Flow Cooler." You will have to count the bolt holes in it and make sure the one you buy has 8 or 11. 1968 has 8, 1969 and later have 11. There's a rare chance you'd need a "short" 11-bolt version from 1969. That's also along discussion. Yours SOUNDS like you need the standard 11-bolt 1969 and later IF YOU HAVE AN 11-BOLT. If you have an 8-bolt, you need a 1968.
The rest comes with 25 years of playing around with these beasts.
