Sometimes, the linkage to the starter gets sloppy or bent a bit. It can cause the switch on the starter to connect before the bendix drive engages the flywheel. The starter will spin before the teeth are meshed. Try a hand file on the lever that pushes the starter switch.It won't take much to slow the switch connection and let the teeth mesh. And sometimes the linkage will never get the switch closed. You can add a bit of weld to build up the lever that moves the switch. Some adjusting may fix the problem. Yes the flywheel can be removed from under the truck...it is heavy, and wants to eat fingers. Will have to remove the transmission first no matter how you do it. It will require the truck be up on stands. You will need some room under there.
