Hi everyone. I have a couple of ducted fan engines that are a bit odd to me. They are Rossi 90 DF engines. I have a large head (pictured) and a small head. I have it pictured with an OS 91DF for comparison. Could someone tell me what DF unit it is made for??? It is a bit larger than the OS engine. I have a few fan units (Ramtec, Dynamax, Byron) and it doesn't fit either of them. The mounting beams and crankcases are vastly different. Any help with identification is greatly appreciated. Thanks...