[Premium-Rx] mixer fets

[engineroom]

Hi Folks,I need to change mixer fets on a Racal RA1792 it has bsv81 type 
on the circuit drawing but i noticed some posts on here before 
mentioning the sd215de's being used the receiver picks up only strongish 
broadcasts stations but passes bite ok i suspect the mixer, it's the 
later 85830 radio with score.I was wondering if there is a superior fet 
replacement or should i stick with the drawing type?
Regards
Steve in Rugby England