There’s one mention of Newt Gingrich in The Reagan Diaries. It’s in Chapter 3, which covers 1983. Page 123 in the book:

“Newt Gingrich has a proposal for freezing the budget at the 1983 level. It’s a tempting idea except that it would cripple our defense programs. And if we make an exception on that every special interest group will be asking for the same.”