With a starving cat no amount of food is too much. Let him eat all he wants but feed several frequent, small meals every day to make sure he doesn't end up with an upset stomach. Also, small, frequent meals make the work of the liver, kidneys and pancreas much easier. Treat him the same way you would treat a cat who is recovering from a very serious illness. If you possibly can, provide food during the night as well.
Right now his body is like a dry sponge, just soaking up all the nutrients from the food. When the sponge becomes saturated his eating will slow down and he will settle down eating a certain amount of food every day.
I've never fed kitten food to starving adult cats and based on the results adult formula foods worked just fine. In three months the difference in the cat's appearance and weight was nothing less than amazing. So I trust adult food to do a good job for a starving adult cat. However, if your vet advises you to feed kitten food, by all means, go ahead and do that. But please do ask your vet for advice.
After this kitty has been with you for about a year, take him to the vet, have bloodwork done and ask the vet how much his normal weight should be based on age, general health status and bone structure. Then, if you have to, adjust the amount of food you feed according to your vet's advice.
That way you can make sure that over time he won't end up gaining an unhealthy amount of weight from long-term overeating but on the other hand you won't try to feed less food than he really needs either.