Ifs crossmember

[eugrides]

I'm installing a speedway mustang 11 ifs on my 53 gmc 1/2 ton long bed and according to instructions they say to keep the truck the same height and rake and level frame side to side,before installing crossmember but with all old suspension and front end removed it's hard to determine height and rake. I still have rear tires on truck .Also do you mount crossmember with same rake/slope as frame any help maybe floor to frame height .