Welcome aboard Biff. First since you are putting the engine in a 71 truck, I don't think we have to worry about meeting emission control standards, but if you have any kind of state inspection you might want to verify that. From 1964 on all motors were built for some emission control and that did limit their performance to some extent. The integrated head is not thought of to highly by most folks. I've read comments that it is prone to cracking and I've read one source that said it was a reasonable head and to run it. The integrated head will limit what you will be able to do with the motor, since the intake manifold and exhaust manifold are cast as part of the head. The 292 also used the integrated head. You can verify whether it is a 292 by measuring the height of the side covers if they are 6" high it's a 292. The good news is that you can put an earlier head on the without much problem.
The two barrel could account for the power difference, there may have been other changes as well. You should be able to get another 20hp with your motor fairly easy with out going to the integrated head.
If it was up to me I'd verfiy that the 79 is not a 292, get a casting number or check the side covers as I mentioned. If it is not a 292 stay with the 76. Look at having the HEI on the 76 recurved to 1963 advance curves. Put an RV cam in it. Can you get the two barrel from the 79 for not much. Find an Offy four barrel manifold with a small four barrel or the 79 2bbl. Another option would be Tom Langdons (Stovebolt Engineering) Holly/Webber with an adapter. Oh and headers.
Larry
