I changed mine on the 83 300sd without any expensive special tools. There are some great step by step write ups on the entire procedure right here on this website that will guide you through the process. Not only will you be able to change the subframe mounts but while you have the subframe down you can also change the trailing arm bushings. For those I used the $25.00 press tool from harbor frieght, or you can rent it from auto zone etc. You will amaze yourself and your friends at how much you can do by using the search function to get the knowledge you need to maintain and repair that 300se!
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If it ain't broke take it apart and find out why.
1983 300SD, 4 speed
1994 C280
1987 300TD wagon
1996 HD Road King
Ride in Peace Eric Peterson, Harley of Macon