Have the intake and exhaust installed from the factory. Noticed the air filter was picking up a good amount of larger debris (bugs, leaves and such), so I decided to add a FilterWears pre-filter, as I have them on almost everything else I have. Took some measurements (5" diam top, 6" diam bottom, 7.5" long). Closest fitment I found was P/N K265 for K&N RC-5100 filter. Rolled the dice. Ends up fitting snug, but perfectly. They did send me the wrong color (ordered red to match the filter), but I'm sure they'll make it right.
https://filterwears.com/products/filterwears-pre-filter-k265-for-k-n-air-filter-rc-5100-57-1058-63-9023-57-9020?_pos=1&_sid=9bb52f367&_ss=r
There are other companies that make pre-filters for RC-5100. Obviously can't speak to fitment of these, but I'm guessing you'd be alright.