Depends how adventurous (and attentive) that you want to be.
I had one of these
with a 1.9 litre 4 cyl pushrod (classic Holden 6 cut down to 4).
I put the thermostat in the lower radiator hose to get the heating/cooling happening the way that I wanted it. The Varajet was leaned off badly, with EGR at idle, and full vacuum advance at idle.
The front grill part was covered (in duct tape to start with, air con tape for second effort...looks like chrome from a distance).
I left the area beneath the bumper free to access air to the radiator, from as low as possible. Removed the cooling fan, and lifted the trailing edge of the bonnet to increase the thermosyphon (of the air system).
The car could be idled for 8-10 minutes in 25-30 degree (C) conditions without getting outrageous. A slow walking pace was enough to get it back under control if the prevailing breeze upset the syphon.
Soo....after long winded post.
I resticted the cooling system while keeping the total cooling system.
Blocking off the radiator in part restricts the total capacity, and should only be used in poor ambient temps.