I wouldn't even attempt to weld it back in. If you've got the tranny torn down to replace the broken input shaft (and drum), then you've got it down far enough to just stuff the internals into another casing. Imagine this: what if when you're done welding it, that area is 0.005" out (towards the block) from the rest of the surface? Think the trans will be aligned properly? Its just not worth the effort IMHO. You should be able to find a good casing for cheap at a scrap yard or local trans shop. I personnaly would reject shipment altogether and get a refund. You didn't get 'scrood', but you did get 'screwed'.

__________________
Jeff Chambers
1990 Mustang GT 10.032 Seconds / 137.5 MPH
14-time Street Warrior World Record Setter
CRT Performance
2001 Tropic Green Mustang GT - 12.181 / 113.2 MPH
2002 Ford F-250 Crew Cab 7.3l Power Stroke - 17.41@77.2
"There's nothing boring about a small block automatic shifting gears at 9400 rpm!"