I think this question is quite difficult. It has a few points.
Firstly, "になります。" is different from "become". In this context, "４回訪れたことになります。" is equivalent to "４回訪れた計算になります。." It rather means "evaluate or calculate." In this case, the moment of evaluation is general.
So, sometimes, なる。 and なった。 are almost equivalent. But, sometimes they have a little difference.
(Both) We’ve found another dead body. The one has killed three in total.
They are basically the same, but there is a slight difference. The former says, "If you count the number, it is three." but the latter is "If you have counted the number at this moment, it is three." So, the latter expects there would be more victims.
やつは3人殺すことになる。 (The future is determined. He is doomed to kill three. Or, an author of a book knows it.)
やつは3人殺すことになった。 (He just got a curse. Now, He is doomed to kill three. Or, he was just ordered to execute three.)
For more realistic cases, imagine a soccer game.
Before a game, you can say 「5点は取ることになるね。(They will score at least five.)」, and while the game,「3点差になりました! (Now they are three points ahead.)」.
Secondly, た basically means completion rather than past. I think French is the same.
"I ate" is "J'ai mangé" ("I have eaten." in literal.) Also, it has several meanings.
In English, “If I were a bird, I can fly.” doesn’t mean ‘Condition: I was a bird.’ た and “if” or “when” have similar, but a little bit different effect.
(Both) Let’s think when we talk about it.
The former is not sure if they will talk about it.
The latter is almost sure that they will talk about it.
(Both) I will tell you when we see next time.
The latter sounds the next time is already scheduled. The former is unsure about when it is.
I think this present form is similar to the English present form. “My flight is at ten.”
Similar thing, happen to “なら”
They would have been killed (not happened) if the car had gone over the cliff (not happened).
Judging from the car gone over the cliff, they should be dead at that time.
In former case, the car did not go over. In latter case, it did.
If the car went over the cliff (not sure), they are dead now.
If the car has gone over the cliff, they are dead.
Now, let’s get back to the original sentence.
If I visit Nara again (which is not sure), you can evaluate that I’ve visited it four times.
If I visit Nara again, you can evaluate that I’ve visited it four times.
The latter is not much different from the former, but yet I feel the speaker is slightly more confident about visiting Nara again.
If I visit Nara again (which is impossible), you would evaluate that I’ve visited it four times.