The Romulan thing is interesting, because we don't quite know where they stand at this period. From TUC it seems like the Romulans and Federation were on relatively friendly terms, as evidenced by Nanclus being in on that meeting discussing rescuing Kirk and McCoy.
Might be Romulans suddenly became friendly when Klingons seemed to be on the brink of launching a war, a most natural development from the UFP point of view - when in fact it was all a devious plot, with the Romulans making friendly gestures out of the left field exactly because they
wanted to provoke the Klingons into war, and the Feds into thinking they could win that war.
The mirror of this would probably have happened as well, with Romulans suddenly getting very friendly with Klingons in order to make them likelier to go to war with the UFP. As for already decent relations, though... Kor in DS9 boasts about fighting the Romulans in the mid-2270s timeframe, so that limits the timeline somewhat.
I think that's not actually established, and not just by Timo standards.
The one thing that may point to the existence of such an alliance is dialogue from "Reunion", where Riker worries about a "new" alliance of this sort. But the word can be interpreted two ways, such a concept perhaps being new as in unheard of...
We're told Romulans are using ships of Klingon design
And in ENT, it's a very Romulan thing for them to use ships of alien design...
It must have been a leap of faith the Klingons started using cloaking technology after.
"After"? In ST3:TSfS, our heroes are no strangers to Klingon cloaks - indeed, when they see a cloak (well, you know what I mean), they immediately assume it's a Klingon one. ENT shows Klingons getting their first taste of that tech in the mid-22nd century already. And TOS has its share of battles where the Klingons are invisible, most tellingly "Errand of Mercy" where the hero ship, prepared for war, nevertheless gets totally surprised by a vessel that fires relatively potent torpedoes yet succumbs to the first return shot, in classic Klingon BoP style.
Timo Saloniemi