I need to build up an area on the rear bellhousing flange of an aluminum block (356 T6)

I had a .875" thick piece of 6061 welded to the casting in order to machine a pad to accept a starter mount (the block originally had no provisions for an onboard starter) but the starter block ended up being 1" thick, so I need to build up this area (aprox. 6" long by 1" wide) in order to match the width of the starter block.

I have limited experience welding aluminum, and that is on much thinner material than what I will be working with here. The machine that I have access to is a Miller Syncrowave 350, and I have just about any filler rod, tungsten grade and sizes available to me.

I'm looking for any input as far as procedure, machine setting, filler rod, etc. to help me be successful completing the job.

Thanks, Dave