Good luck with the build Matezma.

I've made a few lefties for my mates so I know how hard it is sometimes to get parts. Easy solution for the scratch plate is to buy a blank piece of white scratch guard plastic and cut your own to whatever shape you need. I just did one for a LP junior, coping saw, file and sandpaper and yer done.

Its not unusual for some cavities to be a bit under size, but some careful chiselling should do the job. Just take your time and enjoy the journey.

cheers
rob