ive been recently looking at a 350 short block from atk high performance engines......looking for a little guidance this is my first engine build....should i get the short block which is half way assembled or start off with a bare block...the short block im looking at has a compression ratio of 11.5:1 and has dome pistons.............need some help  

If this is your first motor build, go with an already assembled short block. This will save you some time and you won't have to do complicated stuff like filing rings, setting ring gap, crank thrust, etc.

I'd look a a short block with a little lower compression though. With domed pistons, you're gonna end up with really high compression that you'll have to run race gas with. You want a net compression no higher than 10.5:1 at maximum so you can run pump gas, and even then you'll need a hot aftermarket ignition to guard against detonation.  

I agree, the pre-assembled short block takes away alot of the guess work.  What is the intended purpose of your engine?  

im look to put eiether a 350 turbo tran or a 400  behind it with a decent posi rear and drop it in something short body like a regal or a cutlass 80's stlye im looking to make a ten second car  

i would go with the turbo 350 it will fit in that body style easier than the t400. the 200r4 it came with is same length to the tranny cross member and the t400 is for big blocks more than anything.