Space acts as a thermal insulator most of the time because radiation is the only means for a spacecraft to get rid of waste heat. Thermal radiators also only work if they can be oriented that they don't face the Sun.

The exhaust of a nuclear thermal rocket isn't waste heat. The heat from the reactor that heats everything that is not propellant is waste heat. Getting that heat to radiators without cooking people or melting/weakening load bearing structures is the challenge with nuclear reactors in space. On Earth we use literal tons of water and air to the job.

Yes, the trick there is that only MHD coils, and few chunks of tungsten carbide will be anywhere close to the plutonium jet, and most of thermal radiation will be emitted to space.

You'll need some electricity and that's a mere heat generator.

The Carnot heat engine efficiency is not nice at a cold side of 2000K and the working fluid will be a problem. Maybe gaseous helium or argon to reduce leakage, I guess.

The only place I found EU-610 was a Russian thermal rocket. Which is kind of like saying all you need for a coal electrical plant is a lightweight pile of charcoal.

Its a different type of technology, sorta like the difference between burning in a cast iron stove to boil tea, vs using a microwave oven to boil tea.

Sounds like https://en.wikipedia.org/wiki/Nuclear_lightbulb