I looked into this for my Dart block.
Local engineer said you need 2 things....
Emissions test of the engine and a noise dB test.
If they come in under the allowable limits, then you will be able to obtain an engine number to have stamped on it.
Mines got 13.5. but I'll be running E85 which is quite clean on the emissions (bump it up to E90 for a test)......but it would be a laugh running a pig of an engine down low on their emissions dyno. They drive a specific profile of accelerating and cruising. You'd need 6 mufflers too and catalytic converters!!
Not sure if the RTA dyno guy would like to see a few power runs whilst it's hooked up!!