I have a 1989 Chevy Silverado that had a 454 in it. I took out the 454 and dropped a 12 valve out of a 96 Dodge in it. I had read about transmission adapter plates and did not think about one of my options being that I could have just put the engine with an Allison Transmission and modified the drive shaft and been done, so I went through the steps of a transmission adapter plate. The engine is now sitting in the truck with the adapter plate married to the GM transmission but not plumbed in or hooked up yet.

I am having second thoughts about using a GM transmission with the adapter plate.
I have an option to buy a wrecked 1993 Dodge with a 12v and automatic transmission complete for $2500 that I can just pull out and hopefully drop as a single drivetrain with only drive shaft modification in the 89 Silverado.

Here are the questions that I hope someone might be able to help with.
My biggest question is the smog laws in California concerning diesel conversions. How hard is it to get approved from a gas to diesel conversion? Someone told me that as long as you had an older truck and a newer motor that they would approve the swap, but this was years ago in the rules are always changing. Does anyone have experience with this and/or know what the smog rules are in this situation?

Does anyone know if the automatic transmission with engine from a 93 Dodge will fit an 89 Silverado 4-door long bed? I know the engine fits when mounted to the transmission adapter, I just had to notch a brace to make room for the harmonic balancer. I'm thinking about just pulling the engine and transmission adapter plate and starting over with the complete Dodge drivetrain and I don't know if there's room in the Silverado to accommodate the Dodge transmission. If anyone has experience with this I would really appreciate it.

 

I would contact the state before I spent another dime on that conversion.

California is notorious for inane regulations, and I see one hand contradicting the other more than you would think.

Once you have the official regulations, then I think you are doing the right thing getting rid of the GM TH400, while they can be built with enough low RPM pressure, it isn't a walk in the park. Even the 4BT's killed the TH475 with regularity in the P30 chassis.

It should drop right in, or you can find a 94-95 47RH trans to go behind your existing engine and gain torque converter lockup for slightly better mileage.

 

I lived in Cal. for 30 years. The DMV is run by Leftist morons and they try to make things very hard on guys who like to build projects. You should definitely inquire about this swap, but as to who to ask, I'm not sure. If you just go to the DMV you are likely to get an inaccurate answer. Ditto what Pat says about getting the official regs, but I'd try to do that through the Auto Club, AAA, etc. instead of at the local DMV. I'd only go to the DMV as a last resort. If you have any friends who are law enforcement officers now is the time to ask them as well.

 

+1. You don't want to mess with the DMV.

Diesels made 1997 and later are smog exempt. I don't know about conversions. If conversions are like everything else in this state you may be in for a fight.

If you meet with the DMV I suggest getting anything they tell you in writing.