From the looks of things, the only thing that separates the HD'* from the non'* is the diff and the housing. There may be other little things like fiber clutches (non-HD) vs. metallic clutches (HD). And I am pretty certain the torque converter between the two are different as well.

Another thing to look at too. The trannies that came in the Rivieras use a cast aluminum structural side pan versus stamped steel non-structural pans in our cars. Not too sure if this adds to the overal strength of the trans (I don't think it does...it is more for mounting to the subframe than anything), but it does look cool

I personally don't see any benefit in putting an HD under an L27 or L36 for any other reason other than a forced induction conversion. I haven't seen a hp or tq related failure in a 4T60E (non-HD) on this forum in 5 years here.

Umm, i would have to say that willwren is right. There is no need for a HD tranny when staying NA. Mike (95nasta) went all out and his tranny was fine, well except for his very high shift points on the 4t60e and it didnt like thatbut i dont feel that was due to added power. Also i am planning an all out NA build and i am just getting a rebuilt and no HD parts.

Thanks guys.
All makes sense to me.
One thing that may have been overlooked was my question about getting a shift kit installed right now. My tranny is working fine, and I am thinking that the shift kit might help keep it working that way,especially with the mods in the coming weeks.

The tranny has to be fully disassembled to put the shift kit in to the best of my knowledge. But if you want to bump up line pressure to save wear on clutches do a search for "vaccum modulator". You can get it at any autozone or advanced auto for about 17 dollars and installs in about 10 minutes.