Don't get stainless engine bolts, they gall and break easy. Fastenal might be able to get the coated allen head bolts your looking for, either zinc plated or black oxide.
Yes!
Your engine was designed to use steel bolts and screws. If the engine was designed to use stainless fasteners, every bolt would need to be upsized a millimeter or 2 to obtain the same strength as the stock steel bolts and screws. Stainless steel fasteners should be part of the original design, not an after thought. Stainless steel screws and bolts are definitely not an upgrade.
Stainless steel just designates that the material will not easily rust. Many different materials can be blended with steel to make it classified as stainless. Chromium and nickel in various proportions are the two most common elements added to steel to make it become classified as stainless steel.
All of the stainless steel bolt kits being sold online that customers have sent us have been pure Chinese junk. Many of them break before reaching the torque spec. or the threads strip or gall.