Can anyone tell me what position the cam and crank are suppose to be on the GM 4.3 engine? Cam at 12 o'clock and crank at 12 o'clock? Or Cam at 6 o'clock and crank at 12 o'clock? Engine rebuilder sent an engine set at 12 and 12 and it starts terrible and runs poor and will backfire through the mixer and the exhaust both at times on start up. Seems like timing is late. Online automotive info shows that timing is to be set at 6 and 12. Rebuilder claims 12 and 12 is correct. ANY HELP!!!!