340X heads vs late model LA heads vs Magnum.

As was mentioned, the 318 heads have smaller ports than any 340/360 heads. Even with bigger valves in them, you'll be going backwards.

Stay away from the Victor intake. Way to much intake for what you have or plan on. RPM Air Gap is very good.

Instead of going even bigger with the valves on the X-heads, you can revive the valve job & improve port flow with new seats. 2.05" valves are pretty big for your combo. Bigger is NOT better. Just make sure the machine shop knows what they are doing.

Magnum heads are decent, especially with a little work & good valve job. But don't go over 2.02. May not be better or cheaper than going through your X heads. Check the piston deck height first for clearance. While the heads are off, check ring/bore wear also.

The engine is pretty old and you don't know anything about the cam & springs, which may also be old tech & well used. It would be better to just get a modern grind (properly degreed) with springs recommended for it.

Lots of performance can be found in carb tuning and don't go bigger than 1 3/4" headers.

"High stall" converter basically boils down to another mostly unknown component where more performance might be found.