Just to show the potential of a "dog" 383. I worked with a guy who had, from new, a "68" 383 4 speed Road Runner that was consistently into the 12's. What great speed equipment did he employ? All he did was change gears, milled the heads, and richened the original AVS and tuned it. If you think that is slow, look for published times of "as delivered" 440's or Street Hemi's or any other cars from those years.
To Milo3156, Yes, that is how to time an engine, assuming "0" or TDC is accurate. Compression readings just show if there is a problem that will keep you from reaching the engines potential. Learn to tune that 383, no need to change motors unless there is something wrong with it. There is great satisfaction in transforming a "Dog" into a Wolf.