Center of gravity

I'm doing a 4 link , 360 , auto , in my 68 dart. I still have the /6 and trans and front end in the car. I would like to get a guesstimate of where my instant center is going to be before i finish the rear end . My question to you 68 dart 360 sb owners is what frt tire size you have and a measurement from the ground to cg which is about engine cam height at the front spindle. I know there is a lot of variables, like i said just a guesstimate for now which will really help me. Thanks in advance.
Gary.