Recurrent Training
I think everybody should get manual reversion training in the sim during their conversion so that they know what to expect if it should ever happen to them. But because the probability of occurrence in real life is so small it cannot be justified as a recurrent item. If sim time was unlimited then OK, but alas it is not.
Sim Fidelity
I would estimate that I have got at least 20 hrs of actual 737 Classic & NG manual reversion time. All of which was in the controlled conditions of airtesting; ie Classics at FL350/M0.74, NGs at FL150/250kts. I have probably got less than 2 hours of manual reversion time in the sim. In the real aircraft I have done some demanding manoeuvres but mainly just primary control response checks and certainly nothing at low speed or with flaps extended.
My experience of sims in out-of-the-ordinary configurations is that they give you a good flavour of what the aircraft is like, but that they are not exactly the same. Notable examples of this are taxying, first 50ft of take-off and landing, none of which are quite the same in the sim as the real aircraft. The modelling of these features can also vary from sim to sim. The same is true of manual reversion in a sim, it is close enough but not exactly right.
Manual Reversion Tips
I wrote a long piece on this before on these pages, but to recap:
You will probably need to use both hands on the yoke because the elevators & ailerons will be very heavy.
The rudder should still be powered so use rudder (gently) to assist your roll into & out of any turns. Note that L rudder may be reduced depending upon your RSEP status
Just like s/e flying, try to make small changes of hdg/spd/alt early, rather than having to make large ones late.
I dont endorse the earlier suggestion of one pilot for pitch and the other for roll. IMHO one pilot handling and the other monitoring, otherwise nobody is monitoring.
If you are getting tired (it is very tiring), give control to the other pilot for a few minutes to take a breather. This will also give him some handling experience which you may have to call upon for the landing.
When you are on datums it is very stable so you should try and relax your grip (& unclench your teeth!) between manouvres.
IMHO it is survivable, most people manage it in the sim.
S&L