Heater?

[Tony Griffiths]

Derek,
Please excuse my cheek in mentioning, but by allowing warm air to enter the passenger space directly from the engine bay you put yourself at risk of poisoning from exhaust gasses.
Joe

Unless the exhaust manifold and/or its connection to the exhaust pipe are leaking, the only fumes entering the car will be from the vaporisation of oil leaking from the engine and the vents in the valve chest cover. The latter is easily solved - if you so wish - by blanking all but one off of the ventilation holes in the cover plate and fitting a pipe to feed into the carburettor intake.