I have an austin morris sherpa 230 petrol with an "o" series engine. I believe the heater matrix always dissipates some heat and only warms the cab when a slider is opetated releasing a flap cover to direct heat into the van.You can also switch on a fan to this matrix. I want to block off the heater hoses to the matrix. How dependent do you think the cooling system generally is on this heater circuit and would blocking it off cause overheating? The reason i want to do this is because my new other engine is overheating i presume because i have introduced a contraflow in the system by hooking up the old heater hoses to the new engine which although is an o series engine came with its spigots in different positions. I presume this is because the engine is also used in the morris marina,princess etc which i suppose has a different cooling system arrangement. This would be a temporary arrangement untill i have an engineer install a new spigot in the head.
I am not at all familiar with the vehicle in question, however you may want to consider looping the coolant flow rather than blocking it off. Install a hose from the engine heater core inlet to the engine outlet . This will simulate the natural flow and reduce the risk of air pockets which can cause overheating issues.