The only time I would even consider welding the tubes to the pumpkin is if the housing was on a "Jig' so it stayed true. I have seen people weld there housings on the car and it comes out slighty twisted,bent, warped, or what ever you wanna call it, from the heat of the welder. Not worth the B/S, unless you do it right!
As goes for the rest of the parts...
I would recommend 31 spline axles from like either Moser or Strange.... 33-spline for a race car because you can only get the carrier as a full spool at this point.
A good carrier like an Alburn-Pro or Detriot Locker is a very good piece. Dont care for the ARB or the Eaton.
Might as well replace all the bearings while you are there and get C-Clip Eliminaters.
While on the subject about axles you might wanna convert at least the rears to 5-lug if the funds are available.
As goes for the rear-end girdle...I like the T/A girdle,Moser, etc. I even believe that T/A makes them for every one too....(?)
But I can be wrong.
That stuff will hold up in a 3200 pound 9-sec car and live on the street.
Good Luck