I am not positive if this is the correct part number. It is for a Qbus backplane and power supply. Have you ever seen a PDP-11/34 top loading rack mounted box? About the same size! Also top loading. About 10 1/4" high and a 19" rack. BUT, this is for a Qbus back plane with at least 10 slots (there could be as many as 16). And I suspect that the first 3 slots may be ABCD like the BA23 box and the rest are AB/AB also like the BA23 box. In addition, there are 4 * 5 1/4" full height drive bays. Sincerely yours, Jerome Fine