I now own sail no 2757 Helm's Deep. She's a "75 smokers satisfaction, built by Keith Probert. My intension is to keep the boat as close to original as reasonably possible (no hoop). If anyone has access to the Merlin Rocket Book (I'm pretty sure some of you will have a copy!), on page 81 you will find a pic taken from the top of the mast. This illustrates the set up of the traveller on 2957. The traveller track runs parallel to the thwart (not on the thwart), & uses a twin car system, the two cars being joined by a metal strop with a block which the mainsheet goes through to the mainsheet jammer on the centerboard housing.
Is there a way of replacing the traveller with a single car system rather than the exisiting twin affair without losing boat performance? Perhaps a single car with a shorter strop then block?  
Any advice greatly appreciated.

I can't see what's wrong with the standard single car traveller system, this is what I had on a 1960's Merlin once and it was used till recently by Pat Blake.  However not having some system which uncleats the lazy traveller control when you pull on the other one is a right pain.  Harken have some very neat and expensive solutions to this but there are other more Heath Robinson approaches available.

This sounds almost identical to the traveller system we've removed from 2121 except that was a large leg-eating curved chunk of steel presumably curved to follow the boom fitting's course more exactly. The advantage of the twin car is that the height of the central block can be adjusted easily to match conditions and mast bend, unlike a fixed length strop on a single car.It was removed because the traveller cleats and the mainsheet jammer were all non-functional and past repair.
The system on a friend's Sonata gave us ideas - a single car with the adjusting cleats on the car (always in the centre not on the wrong side of the boat) and a fiddle block mounted on the car. The single fixed strop may work with this car - has anyone tried it?
We don't want a hoop as it is out of keeping with the boat and are considering returning to an adjustable rope bridle which apparently was the original set up on 2121 and which we use on other boats.
Other people's experiences would be helpful.

See 'Hoops, Strops and Travellers' on this forum, August last year.  Mags can you provide the link?

I went for a split mainsheet and removed the hoop and traveller.  It does limit the length of the tiller extension but otherwise no regrets at all.

There is 'Hoops v Strops' (members only) in the library section.

I presume you have read Dan's sage advice?

I believe 2789 had a transom traveller originally but it now has a central arrangement without a traveller. The mainsheet is anchored in the centre of the lateral cut out of the main thwart, led up to the for'rd block on the boom, back down to a block shackled to the eye at the apex of an inverted vee strop that has the eyes at the bottom end of each leg hooked into outward opening spinnaker guy hooks bolted to the underside of the ousides of the thwart cut out, back up to a second block on the boom and finally down to the ratchet block and cam cleat. Adjustment to the strop is currently achieved by figure of eight knots to shorten or lengthen it but after reading this discussion and having a look at the boat in the garage it would be possible to provide neat, if limited, adjustment to the strop by leading the legs through a ring which could then be moved up or down by a puller leading down to a single fairlead and jambing cleat on the aft centre of the thwart. Or if more string were required it could be made pullable down through the cut out either side of the centreboard case to 2 cam cleats.

My brother John had a set-up on either 'Baccarat' no. 2614 or 'Tobacco Road' no 2926 which allowed lots of control over the boom angle. He split an IYE traveller into two halves and fixed them to each end of about 60 mm of stainles steel tubing. A strop for the mainsheet was attatched to the two halves of the traveller. The unit could be adjusted up and down the track thus controlling the boom angle very accurately.

Many thanks for your replies - greatly appreciated. 
I can see no point in placing a hoop on this boat as it is not what was originally there. As Dan Alsop says in his rig tuning for older boats - replace the traveller. I'm now planning to look at a full width Harken rail with twin cars & strop based solely on the original traveller thats
on the boat, hopefully to the mm.

2623 is a Smokers Satisfaction that I sailed at Salcombe this year.  She has a deck stepped carbon superspar rig.  The mainsheet comes off a very simple strop/bridle arrangement.  I don't think that you need a hoop to go well or an expensive traveller system.  We did pull the mainsheet pretty hard - so hard on one day that we pulled the block off the boom... but notwithstanding that it was fine.  The set up was very simple, we did not change it all week.  Breeze was never particular light or strong, but for mid range conditions it really was fine.  Frankly had it been windy i think the lack of hiking power compared to the modern boats would have been more of an issue than what the rig would have been doing in those circumstances.

Hope you enjoy it.  We did.