Here are the basic rules in texas:
Which vehicles are required to have the emissions test?
[FONT=Arial, Helvetica, sans-serif]1. Vehicles registered in designated county. Designated counties include: [/FONT]
[FONT=Arial, Helvetica, sans-serif]Brazoria, Fort Bend, Galveston, Harris, Montgomery, Collin, Dallas, Denton, Ellis, Johnson, Kaufman, Parker, Rockwall, Tarrant, Travis, Williamson and El Paso counties.[/FONT]
[FONT=Arial, Helvetica, sans-serif]2. Gasoline powered vehicles. Diesel powered vehicles and motorcycles are exempt from the emissions standards, but are still required to have the annual safety inspection.[/FONT]
[FONT=Arial, Helvetica, sans-serif]3. Vehicles between 2 - 24 years old OR upon expiration of the 2 year initial inspection sticker[/FONT]
since they go by vin, it will say 400cid, i'm sure, but there's probably a form or something to register it as a deisel.