Merlin brain, I am thinking about deckstepping 3376 (Turner NSM4 'Matchless') and am wondering if it would be worthwhile. She currently has a SuperSpars M7 hog stepped rig with raking controls and a strut. I have what I think is a Superspars carbon deck stepped rig on 3236 which I was thinking of planting on 3376, and cutting the bottom off the M7 to use on 3236. The carbon mast is much lighter than the tin one. 
 
I'm needing a new main for 3376 hence why I need to make a decision...the cost of deck stepping 3376 might be nullified by having easier access to good secondhand sails that actually fit the rig rather than buying a new one for the current hog stepped setup. Is this madness? 
 
 

If you're going to do it it's only worth doing well. Some good boats have been destroyed by a half baked deck step conversion that leaves virtually no properly working controls.
 
 
This is not a cheap procedure on the fittings front, you need a good anchor point for the kicker, and the woodwork of the boat needs to lend itself to putting the fittings in the right places. Being one of Jon's boats finding one to copy shouldn't be difficult, preferably another JT or a Kevin Driver hull as they are similar.
 
It may be cheaper and easier to lengthen the Superspar carbon to work as a hog stepped mast and obtain (hopefully) the best of both worlds - more speed on a boat that works. 3268 Raspberry Ripple used to be set up like this, though i think it's now been deck stepped in a multi thousand pound referb. Many boats on the Thames are like it too.
 
If I was trying this i'd fit transverse lowers to support the gooseneck, but keep them non-adjustable and use the strut for bend control. Finding a piece of broken mast to lengthen the tube will be easy.
 
Alternatively still you can make modern sails work on an old style rig. Talk to the sailmaker, if necessary they can re-cut the luff to suit. 

 Not sure I can comment on deck step vs new sails on a hog step, but here are some thoughts based on what I did with 3371 (Turner NSM4 Encore Fume) which I had deck stepped. I thought it made a world of difference; much greater range of rake with a Superspars carbon mast on it plus with a newer set of sails it was (is) a quick boat. Certainly able to win club races against plastic CT's, and it's driver let it down more than the boat did. Whether it's worth it is another debate - financially, probably not - with what I spent on it over the years I probably could have bought a MK1 Winder and gone as fast with less maintenance and hassle - but - it wasn't all about that for me, it was a beautiful competitive boat at club level which I let go at the end of last year to someone who could maintain it better than me plus it needed some more major work - another story (driver again). I was sad to see it go, but glad it's not gone to the breakers. One thing you can't measure though is the tremendous sense of satisfaction you get if you do beat a modern plastic boat. If you want to give an old boat a new ease of life, then why not go for it.

I should follow up on Chris' comment - yes - it must be done properly. I got Ben Dingwall to do the woodwork on mine putting a new post in and infilling the gate on the deck and the Welsh Harp boat shop fitted it out, not a plug there but didn't want to give the impression I did it myself! 

 The option that Guy Winder used years ago on 3161 was to cut the mast at deck level, fitting a female step into the top of the cut-off bottom section, turning it into the deck suport.  This bottom section had a tufnel piece shaped around it to hold it in position at Deck level, leaving all the attachment points for the Kicker etc the same.
 
Transverse lowers were then fitted to the mast to support it sideways.