Your reaction time is um a little weak. Also based on your 60' time you are not getting any traction off the line (or not enough torque).
I am not sure what the compund is of those tires but try avoiding the water box. hard tires are bad enough, wet hard tires are worse.
am also probably not qualified to help. But your welds look similar to what mine first did. I thought I wasn't moving enough wire so I kept turning up the speed. Since I had no clue what I was doing I tried slowing down the wire speed and things worked much better. I also agree that teh flux wire gives you some splatter but it is tolaerable once you get the right speed.
Brapp, I was thinking that engine was set back a little further than normal for a true Scarab, also noted the trans mount looked at lot like mine (which is not a Scarab).
I still don't see any turbos ; )
Interesting to see the details of an original Scarab.
I hadn't seen the Scarab "boost" guage before.
http://cgi.ebay.com/ebaymotors/Cars-Trucks___1976-DATSUN-Z-ORIGINAL-CALIFORNIA-SCARAB-CAR-153_W0QQitemZ220267073326QQddnZCarsQ20Q26Q20TrucksQQddiZ2282QQcmdZViewItem?hash=item220267073326&_trkparms=72%3A971%7C39%3A1%7C65%3A12&_trksid=p4506.c0.m245.l1308
The stainless steel trim should be installed before the windshield goes in the car. And as previously stated, the weatherstrip goes on the winshield before going in teh car.