Technics magnesium tonearm 1200G vs Jelco 850

This is Jelco 850. Don’t know why you asking, but if you want to upgrade stock tonearm you’t better look for something better than Jelco knife-edge bearing design. It was popular upgrade for OLD technics turntables, but the "G" series is excellent NEW tonearm.

If you want some killer tonearm for SL1200G then look for Reed 3p series, it will be definitely much better tonearm with amazing options.

There are NO direct replacement, custom made armbase is required even for Jelco (or anything), but for Reed the armbase on technics can be flat, there is nothing going throught the armbase except for 3 small mounting screws. So this armbase is simpler.