** Power infrastructure provider Solaris Energy Infrastructure's SEI.N shares up 4.1% at $71.07 before the bell on Fri as co poised to join S&P SmallCap 600 index .SPCY next week

** SEI to replace Catalyst Pharmaceuticals CPRX.O effective Weds, Jul 15, S&P Dow Jones Indices announced late Thurs

** CPRX being acquired by Italy's Angelini Pharma in $4.1 bln deal expected to close soon

** Stephens analyst Melissa Roberts said in note she expects passive funds will need to purchase 7.3 mln SEI shares, which implies 3 days of buying demand

** Houston, Texas-based SEI has ~76.4 mln shares outstanding for $5.2 bln market cap, per LSEG data

** Through Thurs close, shares up 48% YTD and 120% over the past 12 months

** 14 of 15 analysts rate the stock "strong buy" or "buy", 1 "hold"; median PT of $88 up from $71 on Apr 10