Filament guife tube is not necessary, plus adds extra and unnecessary friction.
I made a pretty simple but effective spool holder last night.

As soon as I've got it fitted and checked it does actually work I'll post it.
Basically it mounts the spool on the front left hand corner but 150mm in the air and at a 45 degree angle to the bed. So the filement should pull off smoothly no matter where the printhead is.
Takes a couple hours to print (well the way I print it does - maybe double that for most people lol), no supports and attaches either with two strut nuts or cable ties.

As I can't find all the strut nuts I made last year out of the diamond fust filament - I;ll probably just use cable ties :-)

But the less friction between the spool and the extruder the better - particulatly for flexible filaments which have a tendency to stretch and constrict during retractions.

Probably be this evening, gonna have lunch, go shopping, walk dogs ertc - back in workshop this evening.

I printed mine with some godawful flourescent yellow filament from polymaker. It was supposed to be a premium filament - but it's terrible stuff - won't work in my delta at all.
But all my other part spools with enough filament (68gms) would not fit on the bog standard holder.
So it was what i had.
Gonna needs some sanding and filing. But should do the job well.

Plus need to make a back plate - that won't take long. Maybe another 5 gms.
Although I might just use the 300gsm card I use in the laser cutter.