I got a 1983 seville I wanna change the engine I find the 4100 ht very unreliable,what are my options
I agree. I see postings on Facebook where people have swapped out the 4.1L for a Fleetwood. OMG I cannot imagine what they have spent which they will never re-coup what they spent. Hey I may like a vehicle a lot but I'd be damn if I would spend that kind of money. I suspect maybe a rebuilt/remanufactured engine might be better than the original if they put in the welds that GM used in '85 to fix one of the major problems and they may have a better head gasket, I looked at the prices of those one day and they aren't too bad. You of course have to remove the old engine and move everything to the new engine like power steering, A/C, valve covers, etc. I have no idea what a shop would charge to do all that.==================
unless you have Jay Leno type money -
===============What about replacing it with an L26 4.9 Liter engine out of a later model?
Mounting should be the same although I am not sure if (or if not) the ECU would be compatible.