3.58 stroke x 340 main (rods/pistons?)

Have you measured the current cylinder pressure? or
Do you know the exact Scr?
And do you know the camspecs? and
what specifically is the complaint with the current combo?
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Having been running my 367 on the street since 1999, in my 68 Barracuda at 3650 pounds with me in it, I can tell you that, IMO, it makes way more power than the chassis can ever use. Don't get me wrong, it's a lotta fun, but if I was to do it again, I probably wouldn't go with a 360.
Except for two reasons;
1) Lightweight Kb 107s fell in at .012 below deck. So with a quick clean up, and closed-chamber heads, I had a tight quench engine for cheap.
That's NOT gonna happen with a 318.
And with a 340, you'll likely have to mill the crowns off the hi-compression pistons to use a closed chamber head. which ain't happening for free. and
2) the 360 makes a good bunch of low-rpm torque, which if you exploit that inherent capability, you can drive your hiway fuel-economy into the realm of fantasy. And for a DD that is a really big deal.
That's not gonna happen with a similarly powered 340, much less a 318.
So, if that kind of thing interests you, sell the lo-po 340 and grab a good core 360. If you reel in your dreams of big power numbers, you can build yourself a well matched, hi-torque, infinitely better, street engine, to pull 65= 2200rpm, a 12 second car, that still roasts the tires, and if yur fastideous, she might get you mid to high 20s mpgs on the hiway.
That's what a 360 can do for you.
and you don't need a stroker to do it.