Generally you can get easy access to the ones in the back and front for a measurement and close inspection. New/stock they had a large washer and were about 3/4" thick rubber bushing.
At one or more body mount location there will be factory shims to align & square the body and doors.
If/when changing to new body bushings it is critical to use shims as necessary to align the body to the frame for a nice fit....lack of shims and/or improperly installed body shims almost always result in poor fitting doors & door alignment issues.
Its very common for old-original body bushing to squish down and deteriorate over time. The new poly bushings, with a modest body lift, like WH sells are really nice!
EDIT: I just read in another thread where you're having clearence issues w/ your air intake. Here's the answer. This kit is advertised as 1", however taking into account these are NEW bushing, and you're old ones are probably squished down, you will probably see a net result of about 1 1/4" to 1 1/2" of added room under the hood
http://www.wildhorses4x4.com/product/Custom_Body_Lift_Kit_1in