gs engine nos

just bought really cheap a stripped and very tattered gs 150 me thinks.most bits r in boxes.not bad for £40!!!rite engine. i have an engine nos of vs4m!all i came closest to is vs4t!has anyone any ideas of what this is.ive bin surfin nearly 3hrs now but to no avail.o and ive no tax book and cant seem to see a frame nos,badly rusted.were should the frame nos be?