Have acquired what seems to be a very nice a late 1980s Japanese frame. Would like to confirm the frame's date of manufacture.

The frame has what appears to be a plastic cable guide installed on the bottom of the bottom bracket shell. The frame's serial number is mostly under this guide and can't be read with any certainty without removing/rotating/bending the guide.

Unfortunately, the cable guide also appears to be a press-in variety (looks like it's pressed through the normal screw hole with some type of "mushrooming" expansion inside the BB shell. I don't see a good way to remove it. Since it's installed, I don't know if the mounting hole is threaded or not.

I don't know if the guide is flexible enough to bend or rotate it sufficiently to read the frame's SN. It's also in perfect shape, so I'd like to re-use it when I build up the bike. I'm thus a bit reluctant to try rotating or bending it.

Any advice on best way to proceed? Can post a photo or two later if that would help.

Thanks in advance.