I have a customer that has a 1969 AMX .It has a incorrect 390 that is blown,He wants to put a 360 in it until he finds the correct engine.Is there any differences as far as balancer ,flywheel or any other externals?

Externally identical engines.

Incorrect 390? Most '69 AMX's had 390's.

^^^ yup

WHAT?!

yeah there is a HUGE difference...360's have a 4 bolt balancer vs. the 390s 3 bolt...and the flange on the back of the crank are completely different...pre-'70 is flat for the BW trannies...and after is flanged for the torqueflight trans...

not to mention AMCs are externaly balanced...so the balancer/flywheel are displacement specific...

physical block sizes and mounting points are the same tho...