OneWelder

do not make the fish plate stronger than the frame - this could result in a stress point cracking the frame again - ie 1/4 thick frame use 1/4 plate

i am new to this forum

but years ago I Rearranged allot of Trucks I can answer some questions, but not all.

How is this truck setup ? What is this truck going to be used for ? If setup as 10 wheeler dump, definitely go with the 4.10 or lower. I have forgotten the exact number but at approx. 4.00 and below mack used a stronger gear.We Had some expensive lessons with 10 wheelers and gear ratios in the 3.-- S

If setup as tractor we ran A trailer dump for a number of years with 3.87 in it with no problems until we changed it to a wheeler. Wow Big Problems then!