Trying to understand Manifold choices

I’m my humble opinion from working on these 340’s for over 35 years, there are a few small items you can do to a stock intake. And yes, the older 340 cast iron intake the better. 68’ is better then a 73’ due to emissions bosses of the 72-73, again- my opinion.
1) remove the intake to gasket match- helps gain better flow than the turbulence if the ports are off a bit. Do this if you really want to get into the engine and now you can say you did!
2) make sure block off the heat cross over. Sadly it will kill drivability on cold days till warmed up. The advantage is less heat on the carb area.
3) use a plastic type carb spacer. The factory one is only 1/4” thick with a paper gasket on either side but that little bit also helps keep the carburetor a tad cooler.
4) pull the distributor and replace the advance springs with some lighter springs. Check it out and oil the pivot points of the weights. 340’s seem to love a quicker advance curve than the stock set up.

Okay- that’s all I got. I agree if you have a mild or completely stock 340, leave the cast intake. But look out for a LD-340 and if you find one at a good price…. Pick it up.
Good luck and enjoy your 340!
Syleng1