Most steeped grains can not be convereted from starch to sugar (which is what the mash does). A few of the steeping grains can, they tend to be the lighter ones. Grains can be malted, roasted and malted, kilned and malted and roasted, kilned and malted.... If it is just malted, then it can be converted. I think the roasting and kilning prevent them from being convertable. I dont' have my book infront of me, so I forget the exact details of why kiln v roast v both v neither. Suffice to say the more roasted or kilned the darker the steeping will be.
Follow directions with the recipe in terms of the mash and all.
Personally if this is a book recipe, I'd do some swaps. If this is a store recipe (ie they are shiping it all to you as is) then I'd not bother. The reason for swaps with a book is that LME is sold usually in 3.3lb cans, so getting 8lb means buying 9.9lb (3 cans). HOWEVER when stores assemble kits, they put in 8lb, of LME for an 8lb recipe. This recipe is a 'partial mash' because you have to mash the 2-row.