1999 Mongoose SX 4.3 front fork help

Mar 31, 2010
Hey everyone. This is my first post. Glad I found this forum. Just started trail riding last year. Using my 1999 Mongoose SX 4.3. Right now I'm trying to find out what type of front fork I need. I would like a suspension fork but can't seem to find out what type. I've been recommended a 100mm but don't know what my stem length is or steering tube. Plus I have regular brakes (not disc). Any help would be appreciated! TIA.