Get the proper camshaft, and then use a set of Rhoades lifters.
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I've been using Rhoades lifters since the mid 80's.. It took a while for me to buy into them, but they are the real deal. Many other companies make the variable duration lifters, but the Rhoades work the best due to their patented groove for the oiling... They now have some with increased oiling capabilities, but the standard ones will work fine...
I had them in a 72 318 short block with 10.5 pistons. Then I put the top end of my 68 318 on them and it idled at 24" Hg with a stock 340 cam... But when it got above 80° F outside, I had trouble with it overheating due to the high compression.
So I found a cheap set of 360 heads with a fresh valve job and swapped them on with a stock 69 340 intake, and the vacuum was still pulling 22.5" Hg at idle. Still very strong pull with that much vacuum...
Vacuum is velocity, the higher the vacuum, the higher the velocity in the port. VELOCITY IS TORQUE!!!
You can also run a higher rated power valve in the carb and not kick it in for better mileage. I was still able to part accelerate on the highway at 13" of HG, with a 10.5" Hg power valve, so it didn't need to kick in under part throttle acceleration... I was getting 17.75 MPG with a 2.76 axle ratio...
Some people on the board have accused me that they are 'snake oil', but they work. I would recommend them..
Also, if you port the heads, go with making them as straight as possible to increase flow, but try not to open them up too much (area). The more area you get, the lower your vacuum/port velocity will be. Try to eliminate restriction but not open the port area too much.
Then don't over carb. A 600 or 650 CFM will work fine on a street engine...
