I noticed the Marshall LCD70XP 3GSDI monitor listed in the EX1R accessories at B&H says it's for L mount batteries.
Marshall | V-LCD70XP-3GSDI-SL 7" LCD | V-LCD70XP-3GSDI-SL (http://www.bhphotovideo.com/bnh/controller/home?O=details_accessories&A=kitInfo&Q=&sku=672218&is=REG)

Since the EX1R takes B batteries, wouldn't I want the B-mount version of the Marshal monitor?

Definitely order the SB version - the small BP-U30 battery that comes with each EX1/3 camera is ideal for this monitor.