back space

Center would be 3.5" +20 is just under an inch plus add a 1/2 inch for rim lip

just under a 5" back spacing

Here is a helpful link
https://www.rsracing.com/tech-wheel.html#backspace

I always better to have more backspacing than not enough in my opinion. You could always use a 1/4 to 1/2 spacer to lessen backspacing as needed providing you have long enough studs.