can I use a 03 cavalier long block in a 06 cobalt

YES....05 & 06 use the same short block but different electronics. It took me a bit of research with no real answer, so I visually compared EVERYTHING. Found a 04 Grand Prix in the junkyard with a cherry crank for $20 and got the main/rod bearings with it for free. From what I could find, 05 & 06 use different electronics from previous years but still use the same crankshaft however, 07 up use the bolt on tone ring for the crank position sensor. I swapped crankshafts without pulling the engine or unbolting the exhaust, I did the work in a parking lot. I do recommend removing the alternator also to give that extra 2"-3" movement to the right (pass side as seen from the driver seat), for clearance. Took me approx. 16-20hrs, small floor jack, 1 2X4 pc of lumber to hold up the engine, 2 jackstands, & hand tools and some experience. I have to give Chevrolet a pat on the back for this thing, it's a simple, well thought out design that is easy to rebuild, however, cheap is still cheap and that's where the problem lies. I supplied some pics, showing a pounded rod bearing and the lower block cradle. I have been a HD truck wrench for 28 yrs, last 8 yrs with CAT so what I see in cars eventually comes to trucks.......if this helps anyone, then I'm a better person, thank you