The car is a Serpent impact. The very first 235mm car. It should be from around 1993 1994. From 1995 the Impact2 was released.
Conversion to 4wd is not possible. There was a conversion made in Japan in 1994 but I would say it's impossible to track that down. The reason it looks like there is room for a front diff is because the car was made using parts from the serpent 6000 (sprint) series. A 1/8th 4wd car.
For sure the tank in your car is not original. This looks like a 125cc 1/8th tank.
I'm afraid finding parts for the car will not be easy. Even at Serpent I don't think there is much left...
Team Serpent, Xceed, Sanwa, LRP