Will it really make that much difference? Suspension correction really is for bikes made pre '98ish when forks had 80mm travel or less, post '98ish, 80-100mm was standard so suspension correction didn't apply anymore.

Add to that, an older bike will be quite happy running a longer travel fork than originally designed for, I currently have a 1995 Marin, it's had forks from the original rigid to Rock Shox Mag 21 SlTi's (LT @ 60mm) and now some early '00 Rond Magura, which are about 90mm travel, and it has felt good with all the different travel lengths.

For getting a fork, and cutting off the canti mounts, wouldn't suggest it, as unless you are good at metal work, it's going to be messy, and whatever you do, will need a re-paint. There are enough options out there which are disc only, mainly in Carbon if you want to have a specific ATC, plenty on eBay.