Shear strength comparison cast steel/EN40T

Hi
Im new to the forum and engineering so if someone could help me with a challenge in this area I'd be very grateful. I'm trying to understand the shearing forces on a cast steel locating lug on a leading link suspension arm which locks a hub brake back plate on a late 1960's Suzuki scooter in position.

The reason being that in order to make the machine safer I want to fit a bigger brake.

Like the old brake back plate the new brake back plate has a slot in it for the lug (on the cast armature) but in a different position. The new slot position aligns with a bolt hole elsewhere on the casting. So I was thinking I could have a new bolt and nut made up to fit the slot. The bolt will likely have a fractionally smaller cross-sectional area than the cast lug so I was wondering if I could design out the difference through a higher grade materials specification. Perhaps if I turned it out of EN40T.

So can anyone help me understand how to compare the two materials cast steel/EN40T please?
just want to know if this thing will be safe if I go ahead with the plan.
many thanks in advance.

Insufficient information to assist.