What did the manufacturer mean by asking if an angle should be made for the fingers?
When they say 30° degree, I think they mean to chamfer the end of the edge connector for easy insertion into the C64 cartridge slot. 

When they do that, you will probably lose the last mm of copper on the end of the fingers.

If they do this free of charge, I see no reason not to say yes please.



Image from http://www.industrial-electronics.com/et-4e_14.html