Low milage is over rated. I would rather have a high milage car, that I has been taken care of, vs a low milage car that is just entering the area of needing things replaced, like the front suspension trans, tune ups... etc. If you don't plan on selling the car anytime soon, then who cares what the milage is? Heck, I just payed over $5,000 for a 180,000 mile Roadmaster that was modded how I liked.
My 96 Caprice 9C1 has 180k on it, and the thing has never has synthetic. It also, has never been driven easy. Has been cammed, which is harder on the motor... I mean, the thing is still kicking.
If it was me, I would pull a low mialge motor, and drop it in there if the car is in good enough shape to be worth putting the effort into. Like this Roadmaster I just bought. 180k, and I fried a Ring. I wouldn't dream of selling it, or anything like that. It gets a new motor here soon. 180k engine from the 96 9C1. I have faith it will keep going. There is a 96 Caprice 9C1 in the area with 285k on it. My dad drove it when it was at the police department until about 240k. He used to drive it hard everyday he drove it. 120mph down the highway for about 30 miles each way was common. If they were not asking so much for it, I would buy it, just to see how long it went for.
Like I said, low milage isn't everything. Look at my other Roadmaster. Bought it with about 83,000 miles on it. Put about 3,000 miles on it, and the trans blew a front seal, the motor spun a rod bearing(found out the intake gasket was WAY past shot, and it likely was going very lean), the front suspension needs to be rebuilt, the door panels are cracked, and the front seats have a few tears on the sides. I'm still happy with the car, since rust free is so hard to find around here. But my point is that was it a better car than the higher milage ones I have had? From a mechanical stand point, no. Was it considered worth more? Maybe. But I still only paid $2,000 for it.
Just some info to chew on, to help you think about the big picture.
