Make sure you re-use the 318 exhaust manifolds if you plan to run exhaust manifolds instead of headers. Van manifolds are probably b-body manifolds not A-Body and the left side will hit the powersteering box as well as not line up with the exhaust pipes.
The oil pan cannot be re-used from the 318 either, so if that 360 has some kind of truck high capacity pan it may not clear the steering linkage.
I think 75 and newer blocks have thin cylinder wall castings which means a .020 or .030 overbore is the max you can go to clean it up.
That 360 is a better choice than the 318, will make great power on the cheap with a good 4 barrel carb and an RV cam. Don't get too wild with the cam if you plan on retaining those low compression pistons or it will be sluggish to respond. .040 thick head gaskets will put you in the 7:8 to 1 range. Will still pull nicely in a dart though, got the same set up in my Duster.