My first post. Here goes. I have an 83 sedan deville with a 4.1. Right when I was about to have the 4.1 rebuilt, I found someone local with a great running 425 from a 77 deville that he is parting out. I've been told by more than a few people that spending thousands to rebuild a "crap" engine like a 4.1 is simply a bad idea.
I just want to be sure, the 77 425 will work fine in my 83? Will i need to convert or change any set up in my 83 to make this work, or is it a pretty basic swap?
Also, is the 425 a much more reliable engine than the 4.1?
Thank you everyone. I'll get more involved and post some pics of my car. I'm originally from Detroit and my father was an assembly man and machine repair man at Cadillac, so this care is in my blood and has been a dream for me. Its really the only vehicle I have a strong affinity for.

 

Me too I am interested in this type of question!

 

Ok - I know it's been a year since you posted this - but I just found it looking for the same thing. The 425 is truly among the greatest engines ever made. For a while, the 79 Deville (or fleetwood) had the world record for the highest mileage on a passenger vehicle without a rebuild at nearly 700k miles and that was on conventional oil. I've owned 2 and they run incredibly well, plenty of power and smooth. The 425 is the same block design as the 500, 472, 425 and 368 engines - just different bore (same stroke). They did reduce the weight of the engine by trimming from the block overall on the 425 however reducing it's weight by roughly 100 lbs. These blocks are also a nickle composite engine that is lighter than most weighing only a little more (65 lb I believe) than a small block chevy on average - even sized as a big block. I've got a 500 that I planned on using for the same swap, but I'm strongly considering the 425 now instead just for fuel economy and knowing what a great engine it is as well. The difference between the 425 and 500 IS significant in fuel economy
If you already did your swap, I'd love to hear how it came out and anythign you learned from the process!