Don't you have a G5? Is that upgradeable to Mavericks?
Did I have problems? Well.........I knew all about losing any PowerPC apps that I had such as Word and Photoshop. But I had a cunning plan.
Used SuperDuper to make sure that my external FW drive had the up-to-date version of my iMac and that I could boot from it. So booted up from the external and erased my iMac and split it into three partitions - one for SL, one for Mavericks and for good measure Yosemite Beta. Thinking that with this mixed economy I could still boot up from SL if I needed to use Word.
All went well but I didn't bother initially to load up SL in its partition.
Fired up Yosemite....fine. Then I had a look around and realised that there was no iPhoto. Googled and found that a new program was slated for release in a later version of Yosemite. If I wanted to use iPhoto (and all my photos are iPhoto) then I'd have to buy it. -1 Next up, no Pages or Numbers...OK...probably have to faff around with that, find the disc with iLife on but that would take some time. -2. Then I discovered that I had forgotten how useless iTunes v11 is for classical music. -3
So decided to leave Yosemite and look at Mavericks....restarted, option key down, chose Mavericks. Same result as Yosemite so decided to abandon both and revert my iMac back to SL. That's when the problem started because neither Mavericks nor Yosemite would let me see the external drive which meant I couldn't boot from it and so be able to restore my iMac.
Fallback position, stick the SL DVD inside the iMac and install from that. Only. Only the internal drive on my iMac is well-dodgy and the install kept failing.
After a long drawn out process I managed to install from an external optical but by now I'd spent the best part of day.
But probably my own fault for trying to be too clever. Probably if you use Migration Assistant then it will all be hunky-dory.
I'd check whether or not you goal is achievable first. Maybe ask the question on the apple Community support forum?
And I just upgraded my iPod to be told that my iTunes v10 is no loner compatible with it. So I now have to find a way back for the iPod.
Fired up Mavericks ...fine. Then I remembered that I loath iTunes v11 which is mandatory. I needed to pay some bills but all my bookmarks were on the external drive in DSafari and I didn't really feel like hunting around for them.
If opportunity doesn't knock, build a door.