The IVA covers many catagories including HGVs, buses etc. the manual for self build cars is IVA - M1.
These documents are a guide to testers and not a set of instructions for builders so a good deal of common sense is required to go along with the information contained in them.
Don't be put off, if something is not clear, ask on this forum, someone will have an explanation...
http://www.vosa.gov.uk/vosa/publication ... m#P59_1418
Howard