N scale loco coupler conversion questions

[Anonymous]

I saw the posts about MTL's conversion charts, but I am confused...Where the charts say "truck conversion" and "truck replacement," what's the difference? For example, I have 10 LL F40ph locos and all I want to put new couplers on. Rapido on there now...First it differentiates between "F-40 PH (w/ pre-1995 Blomberg truck sideframes)" and " F-40 PH (w/ post-1995 Blomberg truck sideframes)." What does that mean?? Second, Is this just a coupler replacement, or is this replacing the whole truck assembly?? Any help would be appreciated.

Reference: http://micro-trains.com/downloads.htm

Thanks,
John Lardino