I've just received some custom earplugs from this UK firm: https://ultimateear.com - they make a wide range of specialist ear protection as well as earphones for music listening. Mine were for sleeping rather than Morganeering but I think there are several options on their website which could be helpful for driving - including a range of filtered plugs at various attenuation. Their process, which includes arranging for a local audiologist to take moulds, worked efficiently.

My Apple Watch keeps giving me alerts about dangerously high noise levels while driving the Morgan and I think it may have a point. In particular there is a lot of high-pitched noise on motorways (when they can't be avoided) which i suspect may be quite bad for hearing over the longer term.