[Drake] Matching T4x filters for R4C first IF

[Ka9p at aol.com]

hi - 
 
I've found a few references to using T4x filters as roofing filters for SSB 
 in the R4C.  I know that the transmitter filters are 500 ohm, and I think  
the required filters are 1000 ohm.
 
Has anyone seen an article or know what needs to be done to match the  
impedance, or whether being off by a factor of 2 is enough to seriously degrade  
the performance?
 
Thanks, Scott KA9P