I would assume my 4L70E is equipped with a truck bellhousing since I requested that it be be spec'd out like a Trail Blazer SS trans. Does this one pictured below look like a truck bellhousing?
Perhaps your old generic dipstick and tube would work for my car, let me know if you'd like to sell it.
You say you swapped the truck bellhousing out for a Camaro bellhousing, was this for additional transmission tunnel clearance? I did have to beat on my tunnel quite a bit to clear the large stiffening ribs on the top of my bellhousing near where it mated up to the trans case.
On the issue of temp senders, I ended up buying a new Autometer electric water temp gauge and sender to replace the mechanical Autometer gauge I had been using with the old 455. My base model Tempest only has idiot lights for temp and oil pressure and I won't be using them anymore.
The Autometer electric temp sender uses a 1/8 NPT thread and the mechanical sender uses a 1/2 NPT thread. Unfortunately the stock Pontiac temp senders are also 1/2 NPT and there's no place on the LS3 to install one that size.
The plug that I removed from the passenger side head looks to be a 12mm straight thread. There should be an adapter fitting available that will mate the 12mm thread to 1/8 NPT:
The 12mm plug was removed from this location:
