I am about to undertake a project that I would like some advice on.  Here is the situation.   I have recently purchased a house with a basement that has 12 inch thick concrete walls that are only 6 ft tall. The basement also has a dirt floor.  There are no external openings.    I would like to cut open a 6′ bulkhead and use a crawler to dig out some more of the basement floor.  I will then pour a cement floor to have an approx 7.5′ high ceiling.    The exterior of the house is cinder block with brick outside both riding on top of the foundation.   I am planning on cutting a 6’wide opening on the side of the house.  Here are my questions.  Before I cut the opening I am planning to install a lintel that is 8′ long on top of the foundation wall.   Should the lintel be steel?  How thick should it be?  I could also probably have a box steel beam fabricated which I think would be better.   I could also stack together 8′ PT wood  beams but I am leaning towards the steel.   I am going to cut the lintel opening and install the lintel in a matter of hours, but for some period of time the brick and cinder block above will be unsupported.  I cannot think of a good way to carry the load while working there.   I think it will be ok for the short period of time but I don’t know for sure.  Does anyone have experience with this or advice to offer?

Many thanks, Projectman