No. Well, not if you want to do it properly.
Technically racing harnesses should be mounted at a 45Deg angle down from the seat I believe. And that parcel shelf isn't strong enough in itself to hold weight, you can grab it and flex it with your hands. most people who do harnesses either remove the back seat and run them down to the seat belt points at the rear. Or (ideally) have them mounted on the lower roll cage bar (if you have one) or make a bar up and weld that to the car floor to mount the harnesses at the correct spot in relation to the seat and to achieve the angle.
Racing harnesses should be between horizontal and a MAXIMUM of 45deg. The recommended is only 15deg from the horizontal. So in other words, as HORIZONTAL as they can go.
Use at least Grade 8.8 bolts, use 70x40x3mm plates with weld nuts on the opposite side when fixing. Try to mount the plates on a structural surface, and try to mount them so the bolt is trying to be pulled out of the nut (so not being bent).
Really a reinforcing plate(s) should be mounted on the vertical surface of the parcel shelf (so where the back of the back seat used to be) for ideal mounting. Refer to the CAMS manual, or a diagram somewhere on this site for further information.
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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
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