54 gmc -mustang II front. question

[mcafeeswelding]

I have a 54 gmc 100 pick up that i am wanting to put a mustang II front end under.From the information that i have gotten from the numerous companies that sell the aftermarket kits that axle center is very critical when installing these. my question is when you measure for your axle center,you are measureing to the center of the axle or the center of the hub? when you get above the axle and look down on it the spindles angle back towards the cab a little. Just want to get the correct measurement. have the frame with cab still attached sitting on jack stands. am open to options on obtaining the correct measurements. would rather not measure to existing axle it is in rough shape concerned that it may be tweaked from sitting for so long over to the passenger side because of no rim on it. thanks .