This is going to be a long post, I will be right with you.

Hi, I am a professional certified mechanic, with an engineering background, and 35+ years experience. I will do my best to assist you. At Just Answer the deposit you pay is not payment to the Expert, I only get paid if you click on accept. Also keep in mind I don't know if you are a pro or a novice so we may have to fine tune the answer. Feel free to add any additional info you feel is needed as we go on. Always keep in mind that I am here to help you with any questions.

You know I have done some really odd conversions in mt life, I have a fuel injected LT1 350 Chevy in my airplane, and a hot Oldsmobile 455 in the back of a Corvair, so I have pushed the envelope quite a bit my whole life when it comes to engine swaps. So much that I wound up with a machine shop to accommodate all of the custom pieces I have needed to make it all happen. And this is the tip of the ice burg so to speak.

A few thoughts here.......This is what I call chrome ball 101, Diesels are sort of odd, because a hot diesel wont run like a gas engine. I have had this discussion a lot before. Think of a diesel as this giant, say 5 foot diameter chrome plated steel ball, rotating. Compared to a gas engine it doesn't like to rev hard, or high, It takes longer to spin up, and rev, but it will tear down a house if you attach it to the engine and pull. That is the way they are designed to operate. Gas engines are so willing to rev and pull hard like hot rod hard, when compared to diesels engines.

Now some of the newer diesels have lost the big ball feeling, but to some extent it still remains in all diesel engines. The next thought is that when a diesel puts out lots of power, it uses lots of fuel, and they loose their well known high MPG characteristics to a large degree. High horse power rated diesels are really deceptive, because they cant operate at the power level they are rated under load for hardly any time. The high power ratings came on with the ability to computer control the engine. So when you heavily load a hot diesel it will crank out the power, but the second the computer sees the EGT (exhaust gas temperature ) go up it pull you back to the 160 to 200 HP range, but the engine still has great torque, and can pull a load with the HP trimmed way back. So the power output is an extreme variable. The alison trans can be from easy like on a 4 speed 545 model, to expensive, and next to impossible if you are not a total expert on wiring, on the electronically controlled models. I have seen people spend 5K on controlling an electronically shifted automatic. The transmission tunnel size will be a problem for any allison, count on having to do some fabrication on the sheet metal in the floor.

Will the engine and trans fit, yes, I do have concerns that the oil pan might need to be modified, the adaptation of the instruments will be an extreme challenge with lots of custom work needed, and will likely cost quite a bit. If you are a diesel guy, then only diesel will do, I know all about wanting a certain power plant, I have done the same thing many times. But if you are open to suggestions, here are a few thoughts. Look into a 94, to 96 Chevy LT1 350 V8 like was used in the Chevy Caprice (mostly Police cars called 9C1 package) Impala SS, and Buick road master. If you find one of these cars, like an old cop car as a donor car it will give you virtually everything you need to install the engine. These cars got 20 to 23 MPG on the highway, and are fast, with a top speed between 140 to 150 with a 4 speed automatic transmission, and a 3.08 rear end ratio. They also have a large 4 wheel disc brake setup that you can possibly install on your Cadi with some modifications. With the installation of a 383 stroker crank, 1.6 or 1.7 ratio rocker arms and headers these engines will put out over 350 HP, and still get around 19 MPG. I would use the non electronic 700R4 transmission, and the stock injection computer, there are a lot of tech articles on the net, telling how to modify the wiring stock wiring from the factory LT1 Setup. Also adapting your instruments wouldn't be a big problem with this package. If you have any more questions, as always, I am here to help. Good luck with it, have a great day, and Thanks for using Just Answer.

I hope this helps, 100% satisfaction is my goal. Myself personally, and Just Answer are here to serve you. If the answer is not clear, let me know what additional help you need, and I will assist you further. When you're satisfied, and feel you can leave a positive feedback please accept my answer. I don't get paid unless you do. A bonus and positive feedback are always appreciated, good luck and Thanks.

What year and size engine, and which Alison transmission. It makes a lot of difference, let me know and I will try to help you a little more help. With the newer engines and transmissions, the electronics can range from tough to impossible, so it is good that is a concern you are aware of.