Well since you said nothing about a 350ci, I wont say it,"Just get a 350ci and build it".
Ported Stock heads would be pretty good if your capable of doing it. Or a set of vortecs shaved down to 55cc would be GREAT along with a matching edelbrock PERFORMER so you can reuse your existing carb. If changing the carb, which you DONT need to do, step up to the Performer RPM or RPM Air-Gap intake. The intake MUST BE VORTEC SPECIFIC. A Comp Xtreme Energy XE268 cam, 224/230 @.050" .477/.480" lift will work great with the heads and either of the intakes I listed. Have the block bored .030", "0" decked (so the piston are Flush with the deck surface), and buy a good set, such as Keith Black Silvolite's, Hypereutectic FLAT-TOP pistons. This motor, if built properly would be on the verge of 350-375HP. You could end up with 265-285rwhp through a T5 transmission.
Really, you need to do a compression check, and/or a leakdown test. Make sure it doesn't use oil. If it don't, just get the vortec heads, have them milled, stuff the xe268 cam in there, and top it with the PERFORMER Vortec intake and your stock carb.
Then later on, you will have a kickass top-end for a 355ci or 383ci motor when funds permit.
those heads are "083" castings. One is off the crate motor 285hp and/or 300hp, they are the heads with the 90* center holes. These are the one you want. You will still have to have them milled down to keep your compression up. Don't pay much for them...NO MORE than $100-$150 shipped. I have a set like them that I bought slightly ported, They ran 8.5's @84mph in the 1/8 on 360ci 9.8:1 Performer RPM intake, .454" 218 duration cam, in a 85 firebird.
you could also find a used Vortec motor for about $500-$600 bucks at a junk yard, Replace the rod bearings, since this is what tends to fail on these motors, stick a Comp XR282hr and some Comp 918 Beehive springs and retainers on the heads. BAM, you have an $1100 435hp 350ci that'll run mid 12's on STREET tires.
Dont worry about a Vortec having worn cylinders either. I have a 140,000 mile vortec with hone marks still in the cylinders, NO ridge. Looks like new. After personally seeing it, I did some research, and learned that even 300,000 milers in work vans come out like this only to have spun a rod bearing.
Just trying to get you the most power for your dollar.