@AlexanderB
The only plug-in I have seen on the gen 1 prius is the enginer kit.
For exemple
this one
This system may have serious overheating problem in the dc-dc converter.
They use 48v battery and the converter have a lot of job to do, with high amperage in the low voltage side.
They have small power and not regen capability. So you cannot drive in "high" speed during a reasonnable time in ev.
On the gen 1 a good thing is that there is no boost converter between battery and the MG.
But the gen 1 can power a turtle light on the dashboard. I suppose because heating limitations.
This society seems selling an enginer system. I don't know if the quality is good or bad.
The gen 2 have a boost-converter that can handle 22-25kW and peak over 30kW. This is the main power limitation in ev mode. But there is not heating problem in 100% ev mode. The maximum electric power is when using MG1, MG2 and battery, so 33+50+22kW, then in hybrid mode which everybody use.
The MG and electronic components are water cooled via an electric variable speed pump.
The speed limitation without spinning the engine is near 110 km/h. This is MG1 limitation.
Removing the engine in a prius 2 have been made
but is it legal in your country ?.
In Netherlands, for the gen 2 prius, you have some info
here
You probably know this
forum
They talked about the NicoAep system
Maybe you can also find old ev car like 106, kangoo and saxo ?