Rebuilt 3.9l

2000 ls 50,000 on it put new fuel pump new fuel pressure reg.it ran for maybe a min.then bang well you know what happen .so now i need a new motor does anyone out there know where i can get one for a good
price and also when you do the new motor thing do you have to change
or do anything to the computer all help is welcome one more thing because there was some problems in 2000 do upgrades with new motors come with it like i said help me out here thank you