I fitted Magpul MOE handguards to my much modified Marushin XM177E2. I had to do a bit of filing to the handguards, but no real difficulty, using the original Delts ring and end cap. I imagine round RIS handguards would offer no greater problems.
My conversion appears under Model Gub Modification, Modified Marushin XM177E2 => AR15. Scroll down to the bottom of the page.