The regular perfect them form for "he went" is iit. In an answer to this question about two short versus one long vowel, TKR mentions that this form can be contracted to īt. In a text without macrons it looks exactly like the present form.
Are there attestations of it in classical Latin where
- it is clearly perfect tense instead of present, or
- the vowel is necessarily long, or
- perhaps even both?
Given that the present tense can be used for past events in Latin, the first point requires using the context. Perhaps verbs in similar position on both sides are in unambiguous perfect form, so it is reasonable to assume it perfect by analogy.
The only way I can see to argue the second option is scansion. There is a remote chance that the t could be long instead of the i as is the case with hoc, but I find that unlikely.
If someone wants to approach with brute force, here is a list of attestations of it.