Yoka, I don't recall the size of the lag bolts exactly.... I went into a hardware store and bought some for other farm related projects, and the ones I used for the headlight 'repair' were leftovers from that. Almost certainly 3/8" shaft, and probably around 2 1/2" long. Make sure you have big fender washers to spread the load from the head of the bolt.
Start the bolts VERY gently..... don't over tighten them.... just snug them up so the housing doesn't flop around.
Start the bolts VERY gently..... don't over tighten them.... just snug them up so the housing doesn't flop around.