The more you look, the more you find. I have found both of the variations you describe, but the one that you describe as "being caged" is found in a trimmer called a "TRIMSALL" amoung others. If you look close, the bottom of the cylinder is not slanted as in regular RYOBI,s. There is another variation that carries the name of "STIHL" and was sold by them, probably under contract with RYOBI. The name STIHL is inprinted on the plate of an otherwise WALBRO carb. The REED VALVE plate is decidly different, and usually of a ligfht colored material with a flat interior plate, but what I have seen of this production run, they are all long shaft Ryobi sngines. All of the TRIMSALL's I have seen are short shaft engines. I am sure there are other names out there I have not seen. I have two of the "TRIMSALL" versions that I have on electronic ig, and have not experienced the vibration you indicated. I am interested in these particular engines because of the "STUFFING" possibility. (decreasing the amount of open area in the crankcase) Cold weather set in, and my work area is not heated, so have not really had the oppoprtunity to explore these engines, but the one I have running was turning a 18X8 wood prop over 8200 RPM. It has a larger carb, but not much else has been done, I did add additional material to the back plate to futher decrease the open area. I will not run it again without a bigger prop because of the potential con rod problem. I will keep any info I gather posted in the forum. Also, if I can figure out the picture capability of computers, I will try and send some pictures. FLATHEAD 4