Careful with the mineral spirits. IIRC those are petroleum distillates which isn't the same thing as methanol. Here is the UK meths is usually dyed purple ( and they chuck pyridine into it to make it undrinkable - supposedly).
The radiator is probably beyond redemption but $100 for a new chinese one isn't going to bankrupt the owner. If you set up a flush through the send and return hoses you should be able to get most of the crud out of the motor.
Apparently Prestone do a handy flush kit which is aimed at Dexcool users. Wonder how that came about?