The Peculiar License Plate

When I acquired my race car, the first thing I had to do was to get a license plate. The plate I got had a peculiar number on it.

It consisted of 5 different numbers and by mistake when I fixed it upside down, the number could still be read, but the value had increased by 78633.

What was my actual license plate number?

details and assumptions

1. 1 upside down is 1
2. 2 upside down is 2
3. 5 upside down is 5
4. 6 upside down is 9
5. 8 upside down is 8
6. 9 upside down is 6