Shorter acting levorphanol

[HumbleStudent]

SWIM had success with Recemorphon + levorphanol.

My question is this:  Are there shorter acting substances like levorphenol, instead of fentanyl and its analogues?

Basically, shorter acting morphinans.  Please forgive me for my English as it is not my 1st language.
The search engine gives me: The search engine is currently down.  What gives?  Is it something with my settings, or is it at the server end?  Until a few days back, I had no trouble accessing the search system.

[HumbleStudent]

Ok, so here it is... the big step.

SWIM will try it orally this weekend.
From what I understand, 4 mg would be a good dose.
Since SWIM is an opiod virgin, would 2 mg be a good start?
As far as I can tell from Lev's MSDS, the LD50 is around 120 to 250 mg, so that would leave a lot of space for error, right?  So 2 mg wouldn't be deadly?

Anyone have experience, any tips or suggestions?

BTW, it's C17H23NO.C4H6O6.2H2O, the tartrate.