At 00:47 23 April 2018, wrote:
Cheers for the info.

I find without the backrest i'm more reclined, which makes the angle
at
which I need to hold my head worse.

I'm currently having a look at aftermarket 'clip-on' style headrests
designed for older vehicles. The custom shaped foam with cover
solution is
certainly an option.

Thanks.

You could certainly take an automotive headrest and rivet a couple
of tube receptacles to the back of the backrest as mounts for it, as
long as it's not too far forward. The automotive headrest sounds
like a good idea as long as you engineer it to be easily removable for
glider assembly and access to the baggage compartment. There
should be lots available from junkyards everywhere.
RO