I had the same issue as I had to add a larger well tub to the firewall to clear the 327 motor. I made mine out of 1/2" hard felt. It is used in the office world for divider panels between cubicles. Like you, I cut it in flat pieces, the centre hump was made separate and I cut grooves in the back side so it would bend and then used 2 of the same screws I used on the door caps you just bought to attach it to the main part.
If you are interested the material is called Zintra, here is their website,
https://zintraacoustic.com/ Bob J.
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