I used 5mm acrylic.
Maybe consider adding extra blocks of acrylic at the points where it attaches to the bar as spacers to move the blocker back from the roll bar to allow the head rests to fit where you usually have them? Would only need an extra 10 to 15 mm I guess.
Would be interested to see how you get on!
Ken

Ken
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2003 +8 35th Anniv. Model
2014 Porsche Boxster GTS
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1996 Jaguar XJS Celebration