I just wanted to send a "new home blessing" to Kong.
He will be so much happier in his 40 gallon than the 20, and kudos to you for taking care of it right away! It is so exciting to me to see new owners who are so dedicated to providing a good environment for their Uro.
The temp gun and digital probe thermometers will really help you determine the gradient. I am trying to remember what I used on the 40 gallon... I think I used a 100-150 basking spot bulb (depending on the season), and a 60-75 watt "night" bulb that stayed on all the time to keep the ambient temperature in the tank within the correct temp range. You will have to watch your temps regularly, particularly around season changes. The smaller tanks are not as forgiving of environmental changes as larger tanks are, but I think they can be quite workable. 
Congrats again! 
Elizabeth
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1.0 Mali Uro Archimedes (May he rest in peace)
0.0.1 Egyptian Uro Zuberi Mosca Khu (Mosca)
0.1 Sulcata Minnie
1.1 Iguanas Flik and Loki
Madison, Wisconsin