Here's a picture of the short block I just bought. I have pictures at home of my Cub Cadet version (almost identical to the Echo except the CC is single ring) with the crankcase lightened by trimming off the mounting bracket and flanges not necessary for RC. IIRC, the bare block weighed right around 2lbs with the carb. Add a muffler and it's up to maybe 2-1/2. That'll be it for a glow conversion.

That compares favorably to the typical 1.20-1.60 2stroke or 4stroke RC glow engines, especially if you consider the added weight of the motor mount, which the Echo doesn't need. My Saito 1.20S, for example, weighs about 2-1/2 lbs with muffler and mount.

For a gasoline version with elec ignition, you'll have to add another probably 10Oz for module and battery, but that's behind the firewall. These engines are lighter than the Ryobi 31cc and Homelites, and made to a much higher standards with dual counter balance and dual ball bearings. Forged alloy conrod instead of stamped steel. They also cost substantially more, of course.

I can take pictures of it all decked out RTF as soon as I get my other one back from CH.