Is there a Heaven or Hell?

[Siren]

but is there any indication, from a relibable source such as Ra, that Heaven and Hell actually exist?

No. It is my understanding that heaven/hell occur in the time/space portions of 3rd density; specially among those who are biased by these concepts.

4D and 5D, both negative and positive, could also be considered hell and heaven/paradise by 3D perception.

But to answer the question more to the point I think: nobody created such places of heaven/hell to punish/reward the behaviour of 3D entities after death. Each entity is its own judge, and by simple law of resonance, how/what you vibrate makes up your experiential reality; whether in space/time or time/space, in any of the vibratory spectra (or densites) of the creation.

Do we only re-incarnate when we die or is there any time where we go to a Heaven or Hell, perhaps one created by Yahweh?

You could die now, spend the equivalent of what would be 1,000 Earth years reviewing your incarnation and planning the next in time/space; and then just reincarnate back again 2 minutes later in this space/time in another newly born human entity. Or... reincarnate in what would be considered a "past" time; say in Rome, as a legionnaire.

Time is of no concern in time/space. The whole reincarnation concept isn't really linear (or sequential). You could be Albert Einstein in the past and then be a homeless vagabond in New York city now in the 21st century. It is not as if you are "stacking up" reincarnations.