Letting $ t $ equal the number of tickets sold in a single order, we get the following inequality: \begin{align*} 4200&<(70-(t-60))(t) \\4200&<(130-t)(t) \\4200&<130t-t^2 \\\Rightarrow\qquad t^2-130t+4200&<0 \\\Rightarrow\qquad (t-60)(t-70)&<0 \end{align*}Since the two roots of the left-hand side are 60 and 70, the inequality must change sign at these two points. For $ t<60 $, both factors of the inequality are negative, thus making it positive. For $ 60<t<70 $, only $ t-70 $ is negative, so the inequality is negative. Finally, for $ t>70 $, both factors are positive, making the inequality positive once again. This tells us that the range of $ t $ that will result in a profit greater than $ \ $4200$ is $(60,70)$ . Since the number of tickets purchased in one order must be an integer, the largest number of tickets which brings a profit greater than $\$ 4200 $ is $ t=\boxed{69} $.