Commando engine cases. What grade of alloy are they made of?

I have a friend who wants to reinforce his own crank cases by welding on some 1/2" aluminum plate. I can supply him with 5052-H32 or 6061-T6.

I'd like to know which type he should consider. I know nothing about this sort of thing and I work at a non ferrous metal supplier and can get hime some laser cut discs for his application if the types I have will work.

Suggestions? Thanks to any who reply.

I don't know about the alloy, but a word of warning.
When I had my cases welded up after a small crack appeared at the back near the mounting bolts, I took it to an experienced engineer who insisted on immersing the cases in a trichloroethylene ( degreaser) bath for TWO WEEKS! He said that there's always some porosity in old cases and if you just go in and try to weld them oil that is trapped in tiny pockets expands with the heat and can crack them even worse.
He also bolted the cases together while he was welding to stop them distorting.

Bolting the cases together is essential, as is pre-heating them to minimise distortion.

Welding reinforcement to the drive side case is a fairly standard mod on race engines. I've seen all sorts of bits of scrap alloy used but can't comment on the ideal.

Thanks. The fellow doing the cases is racing and he is one of those types of guys who can mill his own parts if needed. I sell aluminum and he asked me which type might be best for a set of cases and I really have no idea since I have no clue what allouy the cases are made of.

If it were me, since I am quite useless, I'd simply buy a set of reinforced cases from Steve Maney but my friend is doing this all himself so I cam here to help him gather some info.

Good call on the porous cases pommie john. Not sure if he's soaking them or steam cleaning them or what.