Removable headshells

I hate to say this, but they all sound different.  You would be well advised to try a few different ones before settling on one.  The one I use is, unfortunately, no longer available.  I do like ones that allow you to adjust azimuth.  In terms of weight, too much weight is not your friend. 

The SA-250 effective mass is 18g, yes? Looking at an online resonance calculator, I would think if you added weight you'd be out of that sweet spot for resonant frequency.

I don't think that you need to be concerned at all. Primary resonance of the moving system is easy to measure so it gets a lot of play. But it is below the audible range so is related to tracking, particularly over warps. I would use a lightish headshell and be done with it.

What really screws up sound quality is the secondary, bell like, resonances of the moving system, which, most definitely, fall within the audible range, and have a much bigger impact on sound quality. Hard for the amateur sleuth, or scientist, to measure.

My greater concern would be the total weight of the tonearm and cartridge and how that will interact with the Linn suspension. Good luck and YMMV.

A heavy headshell ("too much weight") can be your friend if you want to use a low compliance cartridge and need to increase tonearm effective mass.  One very good one that I use with a Koetsu Urushi is the Ortofon LH9000, which weighs 18g, as compared to most of my other headshells that weigh 9 to 12g. I mounted it on my FR64S tonearm, which is already a high mass tonearm, but the FR headshells are not so great sounding. With the LH9000, the Urushi never sounded better.