Can you hook up the HD transmission from an SSEi to an L36?

yes the transmission is the same its only the diff that is stronger on the HD

That'* what I was thinking, so in theory it should last longer than the regular transmission? Take more abuse?

No tranny will take abuse well. Stupid things like spinning one wheel, etc will eat any of them.
When I thought of doing that, I was told that the HD was used cause of the low end torque of the L67'*. The L36 will never make enough torque down there to tax a well running 4T60E.

But what I mean is, I've always thought of the tranny as a weak point on these cars, the HD tranny should last longer than the regular tranny, right?

The gear ratio change is one of the things that makes it HD. Which would mean you'd need a custom PCM or your shift points will be wacky.

I think you're missing the point, there isn't an HD tranny, just an HD differential.
But the HD Diff is a bit stronger than the non-HD thou it will still break if you like to do burnouts while turning corners. If thats what you mean.

Tim, I beat you by one minute.

There is also a different diff housing (at least on the 91-95 HD'*). Some other internal parts may be different as well.

Was just communicating with a couple of seemingly knowlegable tranny guys, and they both said there were no internal differences between the regular and HD. Not so sure about this, so I am still doing some more research.

What are you going to do about the PCM when the gears change?