Dave,
This is from Dave Kirks site;
"Here is an economical alternative to the Bosch Blue coil. The Clone Coil is made especially for us by a major U.S. manufacturer and is an exact duplicate of the Bosch coil in every respect. Featuring the same primary-to-secondary turns ratio and wire gauge, the Clone offers the same
3.2 – 3.5 ohms primary resistance and secondary voltage output and is designed for use on 12 volt systems without the need for a ballast resistor. Internally, the coil is a potted design (contains no oil) and thus is highly resistant to vibration-induced failures. The black color looks perfect on those restored tractors where an original appearance is desired. A bright-plated coil clamp is included and removable double spade connector terminals are furnished on each primary post. This coil is perfectly suited for operation with conventional breaker point ignition or for use with the PointSaver.
Clone Coil price each - $45.00 plus $11.00 Priority Mail Shipping
Found here;
http://www.kirkengines.com/#Products
It might be a bit more pricey than a NAPA coil, I don't know.
Good luck,
Dave