We've had joy we've had fun
We've had sea kings in the sun
But the engines are on fire
And the sea kings must retire 
Don't know if any information would be still needed... if not, well someone else can use it.
Let's start that the Sikorsky S-61 was build in 3 countries - US by the Sikorsky (obviously), England by the Westland, and Italy by Agusta. Only one building them for civilian market was Sikorsky, that produced 200+ of the S-61N and S-61L variants - all have longer fuselage than the mil-spec. The L probably could stand for "Land" as that one don't have side sponsons, nor retractable gear, but can have baggage compartment in the lower part of the fuselage - accessed from the sides (like on the buses). The N (naval/amphibious one) can pretty much float on itself, have retractable gear, and vertical stabilizer at different angle than the L or military versions.
The English version of the "Queen of the skies" was the strangest of them all - those were pretty much license build US military SH-3, but powered by their version of T58 turbine - called the Gnome, had more tail rotor blades (6 instead of 5) and some are exceptionally goofy looking, having outboard long range radar inside retractable, inflatable Kevlar bag... English ingenuity amaze me all the time. They also did non-amphibious assault version called "commando" that had the sponsons and retractable gear removed and replaced with fixed one with emergency floats.
The Italian build something completely different - they licensed the S-61R variant (rearranged landing gear position, long fuselage, and a loading ramp at the back) - that one was made for USAF, as transport and CSAR platform under the name of CH-3E Jolly Green (than with retractable refueling probe - HH-3E), the same variant also was purchased by USCG as HH-3F Pelican (remember, it's PeliCAN, not PeliCAN'T !
). Interesting facts about that one are - those were first and only helicopters to cross the Atlantic without landing, for 1967 Paris Air Show two of the HH-3Es flown from US to France, accompanied by KC-130 tanker - the trip took 30 hours (!), both than flown to Thailand and in 1970, took part in the Son Tay Raid (Operation Ivory Coast) - one of those (call sign Banana 1) was deliberately, successfully crashed inside the prison camp with strike force inside.
The H-3 is still in use in the military, though it is being replaced by newer machines like SH-60R/S in US Navy, or NH90 and AW101 in all over Europe.
Although some users still modify them - the Canadians modified few CH-124 as troop transports increasing its survivability, many details on that are in the 2007 Sea King Symposium presentation, that can be downloaded
here.
On civilian market the S-61 are still going strong... and apparently still be in the future. Although almost all the ones that were used until now in maritime SAR roles, are resold, and modified for utility work. Today we can find 4 types of those helicopters making money - the previously described S-61N and L, and also few S-61R (those are usually modified by removing sponsons and replacing retractable main landing gear with fixed one). There are also many specially modified versions called "Shortsky" - those are S-61s shortened in length - comparable in size to military versions (some actually have fuselage from SH-3s), few were build like that, most are retrofits of the longer N and L. Shortsky have lower empty weight, so with the same MTOW can lift more.
There are many other modifications done to the civilian helicopters - most famous one, are the new composite blades - designed by NASA, then bought by Carson... manufactured by I-don't-remember-who. the blades alone give more payload (about 2000lb more) and speed. Currently Carson is also working on tail rotor and new glass cockpit. Although the main problem currently are the engines.
The T58 turbine used on civilian Sea Kings is the dash-10 version with max continuous power of 1400shp, currently there are talks about certifying installation of newer engines from CH-46 - the dash-16 with max continuous power of 1870shp. The Gnome engines installed on British Sea Kings actually already have around 1800shp, although for some reasons can't get certified for the civilian S-61s.
The lack of OEI power is pretty much the main concern for those machines - and we had an example of it last year during the California fire, where Carson "Fire King" crashed, after loosing power in hot&high&overloaded situation.
Only scratching the surface here, I have some Flight Manuals for the civilian and military versions, if anyone have specific question, will try to answer those...
Unfortunately don't have supplements for the Carson blade kit - if anyone could share that I would really appreciate it.
