Brazos Valley Railroad Society will be participating in the annual fly-in events at the Tesas Gulf Coast Regional Airport, April 29th.   BVRS will be setting up displays in the airport terminal building's conference room.   The displays will include an O-scale layout, an HO-scale test track modular layout, two N-scale layouts (one brand new, and the other built in the 60's), a T-scale "seacoast" layout, and a group of parallel tracks in different scales to visualize their differences.   On the O-scale and N-scale layouts will be engines that have modern sound effects. The theme of the LBX Fly-in is "Planes, Trains, Tractors & Automobiles."   The fly-in events include aircraft judging, precision landing contest, local collector autos, warbird plane rides (for sale), antique tractors, RC aircraft, and model trains.