hi,
personally i,d just fit a new ,horizontal calorifier in the engine bay(ours in in there aswell starbourd side ),i wouldn,t worry about the engine conections ,if your stat,s heathy the pump will fill the coil on the calorifier no problem,1/2 inch as aposed to 1.5 inch full flow.Depending on how far you want to go,with the job ,but you could just leave system as is,and just make sure that the calorifiers full(by running the pump)before you used the imersion,
here,s a link to some calorifiers but i suspect you,ll have seen them before http://www.surecal.co.uk/Product/SureCal.aspx ,good luck what ever you decide