Wow, I was just thinking about this. The leafspring chassis is excellent and you will enjoy driving it.
Now, about the CNG. The 289 has a perfect little space above the differential where the original fuel tank goes. You could hide a CNG cylinder there and nobody would ever know. Since CNG has a relatively high octane, you should be able to build a 289 with 12.5:1 compression and never have it rattle. It should even sound racy.
Interesting idea.
