If you are not building a stock or super race car where they actually check the engine, but just a fast street or bracket car I would recommend you build a 318 with a 4” stroker crankshaft or even move up to a 360.
When trying to buy a 340 short or long block your dealing against the restorers.
There is a ad here on For Abodies Only for a 340 standard bore short block asking $1500.
I have a line on a 340 long block standard bore w/X-heads for $600 locally that I’m buying.
The last time I built a 360, I got one short block engine for free and the second long block was for $100.
When I went to build my motor I found one crankshaft was cracked but the second was good so that was what I used.