Update: The Heli Bars arrived so I could add them as a 2nd 3/4" level of rise, on top of the single layer I have now. Well, I installed the left side first, no problem, very fast / very easy, and no steering contact issues, but ... it made very little difference. Plus, I found that while part of the first level slips over the fork tube and benefits from that fact 'strength-wise', the 2nd level is entirely above the fork tube, and so at that point it's down to only the 2 bolts securing the clip-on and that actually allows for some forward-rearward rotational play ... did not like! ... and it felt to me like I could fairly easily pull up on the grip and prob snap the bolts Hot damn, how exciting would that be while riding?!! OK, I don't actually know why you'd ever do that, but maybe ... accidentally? Nonetheless, since I already had them and was already into it, I decided to continue on and install the right side, 'just to see', but immediately found not nearly enough slack to insert another 3/4" in there. I can't believe how tightly the clip-on fits atop the single riser. There's def no slack for more height. Anyway, even if it had gone on, due to what seemed a very minimal improvement, and with me being concerned about the overall integrity with them in place, I have already returned them.
That said, if anybody else wants to try this ... the 50 mm long bolts included with the Heli Bars are too short, so I bought a 10-pack (fewest offered) of 70 mm stainless bolts from McMaster-Carr ("18-8 Stainless Steel Socket Head Screw M8 x 1.25 mm Thread, 70 mm Long") ... if you want 4 of 'em, let me know.
Prob moving on to handlebars next, after all ...