While a four corner weight review is the ideal way to do it, you can get a good idea of front to rear bias with a simple truck scale. Landscaping suppliers, scrap metal dealers, drywall supply, junkyards, trucking companies, even some drag strips and oval tracks have basic drive on/off scales that can give you a rough idea of where you are at.

I've seen data on the XHD saying they are around 130-140# rate. SS springs range from 130-160#. MP Oval track springs are 120#. Used up stock springs are maybe 50-120#, depending on how abused they were.

FWIW, I believe the baseline Kit Car set up was 1" t-bars, 1" front s-bar and 120# rear leafs. XV Motorsports seems to have found that page in the Chassis manual as most of their level 1 set ups use t-bars in the 1.1 range, front sway bar in the 1.1 range, much lighter (but they wont say how much) leaf springs and a 7/8-1" axle hung rear sway bar.
http://www.xvmotorsports.com/products/detail/index.cfm?nPID=279&cid=2&cdesc=Suspension