What do you use for control and performance instruments while demonstrating power on stall under the hood with attitude and heading indicator covered (No vacuum instruments in 6 packs ) ?
Same as any partial panel work. Altimeter is primary for pitch attitude. Airspeed is secondary for pitch attitude (its indications complement the altitude data, and in a climb/descent it becomes a primary pitch indicator) and also for power setting in concert with RPM/MP.
VSI is generally considered too laggy to use for assisting in fine pitch control when partial panel and is only useful to confirm a stabilized climb/descent, because its indication might be 2-3 seconds behind what is happening at any instant.
Then it's turn and bank or turn coordinator for roll and away you go.
If you were told to do a power on stall in level flight it's pretty straightforward, just hold the altitude by altimeter watching the speed decrease, decreasing the power to get on the back side of the power curve than increasing it along with pitch to hold the altitude until the stall occurs.
If you are told to do a power on stall with a high power setting in a climb, it's a bit trickier because you have to try to judge that your pitch attitude increase is not excessive by the rate of change in altitude and airspeed. In that case you might use the VSI to establish the stabilized rate of climb at the start of the exercise, then add just enough increasing pitch to get a gradual speed decrease from that climb state, adding pitch to maintain that decay rate of speed until the stall.