Thanks for your help. Ended up pulling the gearbox apart and found the problem. Just got to put it back together now lol. Off on holiday soon so it's going to have to wait a week. Here's some links I found that might be useful for someone.
How to rebuild a KM-132 gearbox
http://www.starquestclub.com/forum/index.php?showtopic=148661
Don't believe what you read on the nett. Not all 4WD are wide block. Here's some info about the motors/engines
http://projectzerog.com/transmissions.shtml