I have a 86 Lesabre that has lacked power since the engine was rebuilt several years ago. I'm thinking either they put a incorrect cam in or didn't get the cam timing right. There's no engine check light. I Installed the engine, but I assumed they put it together right. Can the timing chain be accessed and or the cam be replaced with the engine in the car?

The car's been sitting a few years but is rust free and with the price of used cars now, it might be worth resurrecting it. There's probably only about 12000 miles on the rebuilt engine.
JohnD