...but I would be leery of a $300 assembled short block. You never know who did the work, if they did half the things that they were supposed to, etc.
I'm not saying that you have to go all out with the stroker kit, etc., but if you did snag one of those cheap short blocks, I would tear it down and start from square one, just for your money's sake.
You'll have to use a lot of factory parts with a $3500 budget. A stroker kit, even a cast one, will eat up over half that.
Personally, I would find a cheap complete core, then have the block machined as a good foundation...use some CC 4V heads, do what machine work you need to, throw a nice cam in it, good intake and carb, and you'll have a nice solid performer.
Or maybe start with a 400 core...you can turn the wick up on those as well.