Most of the newer model airplane gasoline engines are reed valve engines including "DA", "DLE", & the engines marketed by Valley View.

The reed valve system is convenient and compact to make a easy to cowl model airplane engine.

A rear drum valve engine has greater breathing potential but I'm not familiar with any recent gasoline model airplane engines which have rear drum valves? A variation of this idea is the rear rotary valve but it's limited compared with the drum valve.

The popular gasoline model single cylinder engines of 20 yrs or more ago were piston ported with a side carburetor. The engines were chainsaw adaptations and worked very well but the carburetor had to stick out the side of the cowl.

50 years ago reed valves were popular in chainsaws but not in the last 30 years.