For the conversion check
https://www.pelicanparts.com/techarticles/Boxster_Tech/11-ENGINE-911_Engine_Swap/11-ENGINE-911_Engine_Swap.htm
For the coolant: it may be useful to use an endoscope to look into the cylinders via the spark plug holes in order to be able to narrow down the fault, otherwise you will not be able to avoid disassembly with such a fault pattern imho.