tonearm to fit mysterious pre-cut plinth?

Okay, so it may not be a mystery to you (I hope), but it is to me. I picked up a KM 4001 turntable at an auction. It came without an arm, and I'd like to fit it with one. There's a pre-cut oval in the acrylic plinth, measuring (at maximum center points) 3-3/4" x 1-1/8". Any idea what arm this was cut to accomodate?

I have an MMT arm I was hoping would fit, but it would require major refitting. I don't think the table is anything particularly special, so I don't want to sink a lot of $$$ into an arm for it, but I would like something decent. Any input is welcome, and if anyone owns a KM turntable or is familiar with its intimate workings, I have a couple of tech questions I'd love to share with you... Thanks, Ben
Soundslike the cut is for the SME arms.
It't must be for SME, does it also have two holes at each end of the oval? The M series is the least expensive model in production, I think.

However the 309 and the 3009 are classics and available used here on Agon.
other brands of arms use this cutout, Graham, Triplaner
Thanks!...looks like I'm a goin' SME huntin'. Cheers, Ben