I had the identical problem with my Ranchero. That motor made 10.5:1 compression from the factory. After I had it bored .030 over(429 big block, heh) it would clatter on 93 octane pump gas when I romped on it. I had to run booster or lead additive to keep it from doing that or back my timing way down. I experimented around with the advance springs on my distributor but it never made the clatter go away.
Your timing is way low but I'm assuming you've retarded it to try and prevent the clatter. That has to be holding back your power. I'm surprised it doesn't spit back through the carb on you when you try and crank it. I have a bit more cam in my 289 than yours but I have to run 18 and 38 timing. If I lower my initial much it will catch the carb on fire from the spit back. My advance is all in by 2500 but it still seems a bit slow. I'm considering going to total timing and just running a 20 degree crank retard.
You can see my 65 fastback at: http://hottarod.stangnet.com/
http://members.aol.com/macstang/Gifs/macstang3.jpg
Your timing is way low but I'm assuming you've retarded it to try and prevent the clatter. That has to be holding back your power. I'm surprised it doesn't spit back through the carb on you when you try and crank it. I have a bit more cam in my 289 than yours but I have to run 18 and 38 timing. If I lower my initial much it will catch the carb on fire from the spit back. My advance is all in by 2500 but it still seems a bit slow. I'm considering going to total timing and just running a 20 degree crank retard.
You can see my 65 fastback at: http://hottarod.stangnet.com/
http://members.aol.com/macstang/Gifs/macstang3.jpg
