The J/30 specifications for hoist between measurement bands P is 38' and max foot length to boom measurement band is 13 '. The J/29 uses the same spars as the J/30 but comes in both masthead and fractional configuration with different mast heights and boom lengths. Here are the
J/29 specs. There are some differences so you should check. The J/29 measurement tag on the foot says 12.11 ft so it probably came from a masthead rig and would be short on the boom by about a foot and 9" too long on the hoist.