sat rebuilt 327 cylinder rust what should i do?

i have bought a 327 turbo fire i was told it was rebuilt not to long ago prob is sat under shed with just a tall roof carb was left open so i pulled apart and found it was .040 pistons and look to be new lifters and bearings with not much run time on them well i cleaned engine with brush and kerosine but do too no oil plus dust and if any rain it was sized used marvel mystiery oil and got it un stuck but theres rust on the cylinder walls what should i do someone sail emerycloth and oil maybe tear down and reglazed?

if the walls are pitted bad then its a bore job. if not then you could use a ball hone and re ring it rings are cheap . deep pits with low spots or step marks were the rings sat are hard on the rings so the walls should be nice .rings need to turn on the pistons so i would take it all down free up the rings wash it good and put it back together .sand paper not really what you want to do you could use red 3m scrub pad with some kerosene but its good to have some cross hatch in the bores so a hone would be nice to use

yea see theres all new .040 pistons rings cam/bearings and all that dont reallt wanna bored it any more

Did it run after the rebuild or was it stored right away? If it hasn't run, pull the pistons and hone the rust out. Reassemble with the existing parts and use it. Might not be perfect, but it will probably be okay. Be sure and check the valve faces and seats, too.
Oops, I see where you said it was stuck. The rings are probably toast. Ironic that the better an engine was, the more damage rust causes.