Heat riser/ choke question

Even factory 340s ran a crossover with a heat-riser valve. If you are running into the colder seasons, IMO you need that system in good working condition.
If you are running the stock 318 under that big-port intake, IMO, I highly recommend a small-port dualplane 4bbl intake; It will really wake the teener up. At least it did my 73. No contest; gobs more low-rpm/midrange torque, I thought. I even swapped down from 3.55s to 3.23s, with very little loss in seat-of-the-pants performance.I ran the big TQ, and dialed the secondaries in as fast as she'd take 'em.

Cold engines also like lotsa timing to start the fire very early,to synchronize the peak cylinder pressure where it needs to be with all the cold parts trying to kill the fire. . You just have to co-ordinate the cold timing with the hot-timing and make sure to keep the power-timing below the detonation threshold.
I use (on my 360) a two-stage timing curve, very fast up to cruise rpm (2250 for me), or a little higher. Then I slow it right down so I can burn 87E10 at WOT. It doesn't come "all-in" until 3200/3400, for my aluminum heads, which stay colder even longer.With iron heads you could probably speed it up some.