Researched items can't be used

I have researched all first level options for building the cars, except chassis. But now I can’t expand fit engine or body. I have attached the save file. (49.6 KB)

is this a cost issue? they get greyed out if you cannot afford them at present.

Probably. I noticed someone else posted on this and mentioned it was cost. So it was just I could not access the sub items even though they were cheaper than the main one.