This may be a simple tuning issue. What is the timing set at? And, what distributor is installed. There are several factors that can affect acceleration. If the distributor is curved for an automatic trans [or heavier car] it won't advance the timing correctly. Do you have a good timing light? Does the car ping under load? If not, move the timing up a degree or two and test drive.
Does the rpm shoot up, but the car doesn't accelerate? This may be a clutch that's not fully engaging. I've seen this before, and it was found the wrong pressure plate was installed. The car moved but didn't accelerate very well - it was fine at high speed.
