Your material for the A-arm support holes sounds right,verify the bolts are long enough when you're done. Also locate your grease zerks with it assembled to make sure you can get your grease gun on them- I moved mine just off center.
I'd have to remove body panels to show you the gussets on my wife's but Kliff's post shows them:
http://www.buggymasters.com/forum/showthread.php?t=968
He welded a solid plate on the top where I just welded gussets on the sides and left the center open- I didn't do the lower portion since I sleeved it like you did.-by the way nice job on that. That same sleeve provided the additional support needed for the rack relocation.
The span between the top and bottom rails I don't believe needs additional support, the bulkhead does a good job- haven't seen or read about this area failing.