The Indian test used weapons-grade plutonium produced in the low power CIRUS research reactor, much like how we were making plutonium in 1945. It's thought that Carter banned civilian reprocessing because a nuclear test in 1962 showed that a weapon could even be made from what the DOE described as "reactor-grade" plutonium: https://permanent.access.gpo.gov/websites/osti.gov/www.osti.... https://npolicy.org/greg-jones-americas-1962-reactor-grade-p...

A bomb with an actively cooled pit probably couldn't be miniaturized enough to be MIRVed but it would be compatible with old school single-warhead ICBMs or air delivery.