Back to your question about how it will do when it is cold

Over the years I have run various motors without heat crossovers or blocked off crossovers. Generally speaking, if the vehicle is going to be street driven in cool/cold weather (anything 50 degrees or below), your going to wish you had it. Many engines will not run properly until the manifold has been completly warmed up. Without a functioning heat crossover it may take quite a while for the proper temp to be reached.

I just completed a 351W with preformer RPM heads (no heat crossover). I live in SE AZ and figured it would be no problem, just my luck, a couple of weeks ago we had a spell of unseasonably cold weather . On those 30 degree mornings, I wish I had gone with preformer heads with the crossover as it took about 10 miles before the car started running well.