Problems with starter on 87 Chevy S15?

Bought truck and guy said it may just need a starter put on it and it will run. We put it on with all types of shims and cannot get it to crank motor over. It acts like it is going to for a split second and then stops. We took dist. cap off and turned front of motor to make sure that timing chain was not broke because when it would sound like it was trying to start, I never seen the motor move. The guy mentioned that he had put a new flywheel on it and it looks good. Could he have put a different flywheel on there than it should have and it would fit? We had the starter off and hooked to battery and it is engageing it seems like. The guy says it is a new starter that he bought and gave to daughter's boyfriend to put on when it would not start at one time. The starter does not look new. Can the starter appear to be doing all right and not engaging far enouph? Thank you for any help you can give.