Maybe I don't know how to install an intake manifold correctly!

Recently I found that the reason my 440 was running so poorly and wouldn't smog was because I had an intake manifold leak. The smog tech discovered it by testing it with a smoke machine. I was the one who had installed the cast iron intake, so obviously I screwed up, but I'm not sure what I did wrong.

I also installed the intakes on my other Mopars (360 & 408 LAs), and now I'm wondering if I might have made the same mistake on my other engines.

So, two questions, please:

1. Has anybody got any suggestions for avoiding leaks when installing an intake? and
2. Any tricks for doing a smoke test on a carbureted engine? I've only seen it done on F.I. engines, and wondered if any different smoke test procedures apply to a carbureted one.

Thanks, guys!