Agreed. Slugs for the 273 can be pricey. Egge machine will make some for you, but there cast pistons. Nothing wrong with cast pistons, but, they do have there limits. If your building within those limits and driving like a normal person would, they'll last.
A bigger engine is a worth while investment. IMO, I'd skip the expensive 340 engine. (However, if that is what you want, don't let anyone talk you out of it.)
I would look for a 360. There alot cheaper and have a bit more stroke for alot more torque which is great for the street. There a easy engine to build up and 400 HP can be done easy and very streetable without huge stall converters or cam sizes.
This makes the engine work less per CID and alot more fun while driving.