Beta Gavril Grand Marshal V8 Twin Turbo 0.63

This update brings this mod to 0.11 standards with (perhaps a slight overkill of) exhaust flames and stuff.

This update fixes the fact I based the previous update on outdated jbeam files. The automatics now have torque converters and the manuals flywheels. I also added a drag automatic with transbrake. I hope I actually got everything right this time.

Apologies for the late update, I wanted to include extra parts but I sadly don't have the time to finish them, so this update does not include any new meshes.

Since people requested more gearboxes, I added... more gearboxes!

What's new?
- 6-speed automatic from the D-Series
- Gearbox with the ratios from the T56 transmission from a Camaro
- "Long ratio" gearbox with the ratios from the T56 transmission from a Viper
- 3.15 rear differential to go with the D-Series automatic
- 2.73 rear differential to go with the Camaro T56
- 3.07 rear differential to go with the Viper T56
- Adjustable race rear differential for those unhappy with my own choices...