I had a Naish Boxer SLE back in 2007. I think the bar is the standard bar for Naish SLE kites from that year.
Check this link: https://www.mackiteboarding.com/boxer07review.htm
and scroll down to the bar photos.
If I remember it right, Naish had some versions of the bar with different length of the depower stroke and also a version with five lines. You can easily rebuild that bar to fit any modern kite that flies with a standard four line low Y setup (=most kites). The chickenloop is a push-away release that works just as on any modern bar, even if I don´t like those neoprene covers that makes it hard to see if something is about to break. The depower system with the pull-pull straps is also fully functional as long as you don´t get too much salt on it and is made with metal parts that lasts forever, if you keep track of corrosion. Some of those Naish bars from that Era came with what they called a "mini 5th line" as a leash, which was just a fixed line that was connected to the top of the depower system, meaning that it had no flagout. Basically a classic suicide freestyle leash setup.
First, check how long depowerstroke you need for your kite. If you don´t know, try with a long stroke in light wind and get a feel for where the limit of depower is for your kite and then shorten the depowerline accordingly. Before you fly, check that all four lines are of equal length if you put the depower on maximum power. If they are, your kite will fly as good as with any bar. For your safety, make sure however that you have some kind of flagout leash (a double steel ring on a pigtail is probably the easiest in this case if it isn´t on the bar already) and that the push away relase of the chickenloop still works under load. If you have any problems with the chicken loop release function, you will need to replace that.