Beside its reliability, the SP 27** series is known for one thing: being a heavy brick... ;-)
Providing a sturdy mount for a 93lbs cuboid on/around the dash fairing, with or without utilizing dash shelf, might be tricky...
Over here riders often chose the top of the handlebar-covers as convenient location.
Clamping a RAM-yoke on the h/bar tube right between the original mounts on the upper triple-clamp, creating an appropriate opening through the centrepiece of the plastics (where that Honda logo is placed) and then another RAM-cradle to hold the unit seemed the most solid way of installation, while providing the compromise of not conflicting with a tank-bag nor with operating the key in the ignition-lock.
Routing the cables for on-board power supply and audio-out out of sight along the switch harness and inside the handlebar-covers gives it a neat finish.
Another ingenious way, suitable on post '96 ST's was an L/V-shaped stainless steel sheet, fixed onto the top surface of the handlebar-cover by 4 well nuts (as used on windscreen/garnish), and the cradle bolted to the other leg. Wiring hidden underneath/inside gave again a neat appearance, nut as sturdy as the RAM-joke on the steel bar, but still...
I've seen installations on dash-shelves, but due the lack of internal structures combined with the weight added, the unit will start to swing/vibrate, making it difficult to read and may cause internal damages/contact issues on the long run...
I also wouldn't place such a device on the handlebar, its probably obstructing safe operation of the bike plus it sits very exposed up there, not only to the elements, but to getting smashed during a tip over (which I'd once observed happening to a 550, getting shattered on the upper edge of a trunk-lid during a tip-over happening in a parking spot... screen cracked, housing abraded, pieces of the cradle all over the place... not an ST though...)