89 model CR250R Honda bike cylinder.
If you took a stock unported TRX250R cylinder & compaired it to the stock CR250R cylinder, the CR cylinder porting would be like an upper midrange ported TRX cylinder. Kinda play drag right straight from Honda.
You could mount that cylinder on the TRX bottom end & from the pics, looks like it was at some time because of the red high temp sealant in the P/V workings hole.
Its hard to see in the pic, but is the P/V still in place in the cylinder ??.
Pull one of those caps off the side & see if its still there.