Engine Balance Question 1995-1996 3100 M

[JoeMechanic]

I recently installed a 3100 M engine in a grand am gt 1995.I installed it and hooked up the trans..460TE or something like that bolted the flex plate with torque converter 3 bolts.The question I have is this..I know its probably balanced at the harmonic balancer and or crank shaft but does this engine and transmission setup need to be installed correctly at the flexplate?.By this I mean do you have to mark with paint or crayon before unbolting at converter/flexplate union?(old engine) and installed the same way?.I didn't notice any weights on the flexplate as on my 400 CI chevy caprice engines flexplate so I assumed I didn't have to worry about this motors balance at the torque converter so I just installed it as I lined up the bolt holes on flexplate.I think I am ok but I have a problem with hesitation/stalling at stops and shaking at idle and shaking offline until reaching 1500+ rpm as if it was running on 5 instead of 6..read my other thread.I am just asking as some of you may have more experience with the 3100 M motor than I have..thanks for any advice,Joe.

[gpse3400]

The engines are internally balanced. It is good practice to mark your locations but no you don't need to. Bolt it up and run it.

[JoeMechanic]

Thanks man..thats what I thought.

I marked the old engine with paint on flexplate and torque converter but I installed a new/used bone yard engine.I am just trying to figure out why it shakes and hesitates 1000- 1500 rpm or until I reach 40 mph or higher..its got me thinking I bought a crap motor and 1 cylinder isn't firing correctly due to a burnt valve or something.I am looking for the compression specs and will do a compression test in about 5-7 day's from now..I'll give it a chance to run a bit,Joe.