72 340 build vs...other options

My take.
340's are cool nostalgia, If I had an all original 340 equipped car, yes I'm keeping it. If I happen to have a 340 around by itself I'll sell it to someone who'll do more with it than me whether it's a restoration or is really big into nostalgia.
360's especially 5.9's you can "do more with less" so to speak. Or go with the gusto: 408 stroker based on a roller LA 360 or 5.9 magnum.
Like I said, I like 340's, my favorites are the roller LA 360 and the 5.9 Magnums.
And 318's are not my most favorite but will still run them as I think they are great general purpose motors, I have a lukewarm disposition about them.
I only owned one 318, was a real good motor, gave me little to no problems just had a ton of miles when I picked up the truck I used to have (est. 290,000+ miles). Until I replaced it with a low mile 360 from a wrecked 1991 Ramcharger as it was starting to burn oil and had really bad blowby. Still pretty good considering that 318 had a hard life.