Cassette quest. add 11-34 instead of 11-25
I just received my new Surly Cross Check with Tiagra and bar end shifters. In order to get better singletrack performance, I want to take off the rear 9 speed 11-25 cassette and dérailleur and replace it with an older MTB 9 speed Shimano Deore LX (RD-M571-SGS) dérailleur and a SRAM PG-950 9sp 11-34 cassette.
My question is whether the Shimano Bar-end (SL-BS77). 9-Speed Dura-Ace shifters are compatible with the MTB derailluer and cassette? Also, will I need to lengthen the chain going from 11-25 to the 11-34?