One of our club members fitted a section of carbon fibre tubing to his Model 66 as a barrel sleeve and it looked dead smart. It probably came from an old fishing rod
Another fitted some narrow pvc black pipe and then added some tight fitting black plastic mesh tubing to it and that also looks really good as well. You could also check to see what types of decorative heat shrink and self adhesive vinyl are available - or just spray it matt black.
Some shooters prefer not to have the barrel weight fitted as it is quite a heavy rifle for some shooters to manage and it also suites those that prefer the balance of the rifle to be closer to the body.
Any tube that fits can be used but a choice of tube materials can make the rifle feel quite different (eg pvc/alloy/plastic/steel) and when fitted they are quick and easy to swop around.
Some of the original steel barrel tubes were glued-on in the factory and if you have one of these the glue may have spoilt the finish on the barrel.
Tubes with a bore that is a little too large can also be made to fit well if some suitably sized "O" rings are used between them and the barrel.
There is no need to glue the new sleeve onto the barrel - it is far better to keep your options open so you can try the rifle with no sleeve weight at all or test and try various options to find what you like the best.