Knock in my 3400, need advice

[over40driver]

I bought this silver 2002 Alero coupe brand new in 02. Put 75.000 miles on it and sold it to daughter in law. Recently it was sold to 18 yr. old grandson which in 4 months proceeded to add 4 new durn holes to the interior. a nice sized dent to the pass. side bottom front quarter panel, then the oil pressure gauge started pumping oil out. At midnight on the way home from work, he drove till it knocked. The next day I went over and repl. the sending unit and added a gallon of oil. It has a bad knock when you first start it but runs good down the hwy. Im thinking a new crate 3400 but am also watching my budget. Am going to restore the car back to orig. beauty, as close as possible. Any advise on the best place to get a GM crate motor?