I changed my mainsail for one which, from your description Suibhne, sounds pretty much the same design and with the same fittings that you are considering. Mine was made by Kemp Sails using the measurements that I had supplied, and they did an excellent job which I can highly recommend. The sail is fitted with five full length battens and has Rutgerson wheeled slider cars. The Selden mast is the one that was fitted to my B36 from new and I have had no problems or difficulties feeding the slider cars through the original slide gate, and I can confirm that none of the boats hardware either needed to be or was changed to suit the new sail. Fitting the battens is more complicated than was the situation with the previous partially battened sail as there are small nuts and bolts involved in securing the slider car fittings once the battens are in place. I've found it easier by placing some self adhesive tape over the fitting where the nuts go as this holds the nuts in place while the bolts are fitted and prevents the nuts from dropping out and bouncing overside.
Once all in place the sail has worked like a dream and allows me to sail closer to the wind than I could with the sail it replaced.
So, in answer to your questions,
Any pointers - go for it!
Any warnings - fitting the battens takes a little more care than I needed when fitting those on the sail I replaced and is a little more time consuming. Also when I remove the sail during the winter lay up, the battens are too long to store in any of the cabins, so I take them home where I can store them straight in my garage.
Lastly if anyone wants a secondhand partially battened sail for a 2002 B36, I'd be happy to let the old one go for £150.
