Heat riser/ choke question

You're talking about the exhaust cross over, not the heat riser. The heat riser is located in the passenger's side exhaust manifold and closes on cold startup to aid in fast warm up.

The exhaust cross over IMO should be left unblocked on most street cars that are driven every day, or several times a month. The cross over helps atomize fuel and also takes a part in proper choke operation as you've already said. I am unsure if you can adjust the choke so that it will work to your satisfaction with the cross over blocked. You can certainly try.