1998 Chevy Lumina how to check for timing

1998 Chevy Lumina 6 cyl 134579 miles

I replaced a engine in the vehicle and now it rotates but wont start, there are no marks on the crankshaft pulley to indicate where the setting should be for TDC im getting spark and fuel so as I believe the timing has jumped or the belt is broken. Any suggetions on what to check or how to check the timing is greatly appreciated