Don't forget that the 157M is a channel frame style choke, so the base is in the middle of that 1.75 inches. In other words, if mounting on top of the chassis, you can gain some separation from the power transformer by letting the bobbin overhang the edge of the chassis. If mounting under, you would, of course, have to relieve the base to add clearance to move it over. Also, if mounting under, remember the transformer doesn't go as far outboard as the stack does on the topside - it might be that the choke bobbin flanges would land in between things under the transformer and allow placement without a base relief pocket.