I checked those bolts and the strenght rate is 8.8. It seems to be the most common strength rating in the bolts which are available around here. Any special bolts needed then it is going to be a special shop over 100 kilometers from here.

8.8 is standard and 13 is commonly 'hard bolt' used on some places, don't know if it matches specs of 300 but that is how it seem to be in car repair shops here.

Anything lower than 8.8 is probably coming from china and can't be used for anything really

Good progress

Can't wait to get my project started