I have done this to my 92 Marin (1 1/8th HT) with mixed results.



First I added a cheap old Suntour (SX I believe) fork from a 26" Trek Hybrid someone gave me for parts. Not the best, clunky, low travel, but it did smooth off the impacts a bit. It actually rode pretty good but the geometry was thrown off for steep access climbing (it wanted to lift the front tire too easily).



Then I got a 26" Rocky Mountain parts bike with a Marzocchi Bomber fork and added that to the Marin. Better travel, less clunky, but even more hard to ride up steep access hills (front end gets very twitchy at slow speeds). The fork is a little longer. One project this winter is to SS the bike and work on reducing this issue. What's nice is it has disc mounts and my rims are disc ready so I can throw the V's on the back and 180 disc up front.