thanks for the thread so far and it helped me on my own quest (sorry to be a bit long-winded)
I am a new owner of a VX Limited 1991 HDJ81 and wanted to put together a backup alternator.
I took out my running alternator and measured all the outer dimensions to go searching for a used one with the round 3-pin plug.
Bolt holes centre to centre:160 mm
Lower anchor width 58mm
With alternator resting on pulley on a flat surface, Anchor forward edge to forward edge of pulley: 56mm
At my local wrecker I found a pile of Denso alternators, three of which had Toyota labels with the red 12V on it.
I found one with the 160mm bolt hole spread, except that the back end with the soft aluminum cover was oriented 90 degrees clockwise compared to mine which has the pos terminal in the vertical position (this turned out not to be a problem). It had a pulley for the flat belt, not the V belt.
I bought a Toyota double V-belt pulley online, part number 27411-17030
I clamped the flat belt pulley in my metal vise and got the nut off with a breaker bar (I am told an impact driver will do it more easily but I don't have one)
Fitting the new pulley I tried to follow the FSM as closely as possible and duplicate the special tool illustrated.
I drilled a hole in the back of a ½" drive 7/8" socket to allow my 10mm long socket to turn inside of it.
Ground two flat surfaces into the big socket so it wouldn't turn in the vise:
Let the alternator sit in it with the pulley facing down.
Turned the alternator shaft anti-clockwise on its 10mm hex portion using a 10mm long socket from below. I didn't get to 110 Nm but I tightened as much as I could until the 10mm socket split apart.
I am still experimenting with building the right tool using an impact driver 10mm socket for the next time.
I have worked on Bosch and Hitachi alternators, all of which have keys on the shaft, but it seems that Denso go to a lot of trouble to tell you not to turn the nut on the pulley but to squish the pulley between the nut and the bearing.
I put a number of paint marks on the shaft, the nut and the pulley to let me check from time to time for any slippage.
The number on the wrecker alternator is 27060-74080. I hope those last two magic digits mean 80A. It is a bit longer in the back and heavier than the one that was on the vehicle which makes me suspect it has a higher amperage rating.
Fitting it was no problem. The round 3 pin plug went in nicely, the positive wire reached the terminal ok. The unit being a bit longer in the behind didn't matter.
Startup showed 12.48 V to begin with and fingers crossed, soon reached the 13s, steadying out at 14.3 V.
Mandatory retightening of belts after first few starts and a bit of belt screeching.
Successful experiment!