You won't be swapping internals at all will you? Either the REBA uppers fit into the SID lowers or not, first off measure stanchion diameter, if they are the same then try it, I did similar with some Manitous a while back and never had an issue, if it doesn't work, you'll find out soon enough and doing an upper swap will only take 10-15 minutes anyway (2 bolts to undo and do up!), it will take longer to research all the options!
Impoverished weight weenie wanna-be!
Budget 26" HT build viewtopic.php?f=10&t=110956