I'm mounting different toilet tank on an old bowl. What is the mounting bolt spacing of a typical toilet tank? By this I mean the 2 bolts that attach the tank to the bowl.
There is no spacing standard, friend.
Tighten all them by hand first then go around and tighten them until you think its good. You don't wanna tighten too much because it'll break the toilet. After you tighten them check 4 leaks. If it leaks then tighten them.
The tank will always have a little wobble, unless its installed close to the wall, so you'll want to ensure if its free standing, meaning nothing is bracing it, tighten it to a degree that there is a bit of stiffness in relation to movement and you should be fine.
You're talking about 'tank-to-bowl' bolts spacing. I think the span, 6 inches, centre to centre, has been standardized within the industry for a long time now, maybe for the last 40 years? If you're not sure, measure them first.