[Barnsnake]

If you have an external starter solenoid, it might close (hence the click), but not contact. A voltmeter on the downstream side would show whether it is contacting.

Another possibility is the lack of an adequate ground path from the engine block to the battery. You need a dedicated ground cable from the block to the frame, since the motor mounts are not conductive. The negative side of the battery also needs to be connected to the frame. Remember powdercoating and paint are insulators. Clean the cable connection locations with a grinder or sanding disk and use star washers on those connections. You can then re-coat with something to prevent rust.