In a high compression engine with oil and coolant passages I might be more concerned but in this 14HP low compression engine that I don't think has been apart before I think these bolts will do just fine.
However, if they looked or felt suspicious I would replace them. I think they are grade 8 or grade 5 it's hard to tell with these for some reason, regular 3/8" bolts.
Before I retired I was a mechanic at a chemical plant and when it was taken apart for the yearly shutdown maintenance all but the largest bolts and studs (over 2" diameter) were replaced even if they still looked good.
The large ones were thoroughly cleaned then checked by an engineer and had NDT checks done to check for cracks, stretching, corrosion etc.