To give ya some perspective, the 216 in my 51 went over 90,000 miles without a filter before I tore it down due to restoration. Still ran great and didn't use much oil. The 216 in my 50 has gone over 68,000 miles and still doesn't have a filter. Pulled the pan last year to clean it and adjust the bearings and the bearings and crank were in fantastic shape.

If you find a filter go ahead and use, but I wouldn't lose sleep over it. Just change the oil at least every 1000 miles.