White smoke!!

I have a 1978 MG BGT. It has undergone an unleaded conversion and there is white smoke coming from the exhaust. My local MG specialist shop tells me this could be a result of the brake servo malfunctioning and this being burned off - a problem he has heard of before. Though I have spent £1000's on the car, I know nothing of engines - I just made it look nice! I am a complete novice when it comes to any moving parts!!!Is what he is saying true, or is it time for a new engine? Appreciate your help

Not necessarily a new motor, but possibly a new head gasket and maybe a new head. Are you losing coolant? Is the car running hot? Check out http://www.mgcars.org.uk/
Does the exhaust smell like coolant? Did you have work done on the brakes at the same time you had the head worked on? Are you losing brake fluid? Is there another shop you can go to for a second opinion?

I agree with Kim. Sorry to say...head gasket for sure! Don't dispair...not a tough job if you have two or three wrenches and a new valve cover gasket.