Cartridge/arm matching

You should get a test record. I use the Shure Era 4 obstacle
course(about 20 bucks on Ebay). It has a test for tone arm
resonance to test your arm and cartridge compatibility. You can
also get a Technics 3 gram headshell weight,if you need to add
mass to the arm (about 5 bucks on Ebay). These are very
inexpensive tools you should have if you are into vinyl.

The Dynavector 10X5 would be a great fit on the RB250. You wont miss the shelter. IMHO.

Rega RB 250 effective mass is 12g
and you know the compliance of your cartridge @ 100Hz (Japan standard)
make sure to multiply it on 1,5 or 2 to find out actual compliance at 10Hz

and then simpli check the diagram illustrates the relationship between cartridge compliance, tonearm mass and the resulting resonance frequency:

http://ortofon.com/hifi/support/cartridge-tonearm-resonance-frequency

you will see which cartridge (compliance @10Hz) will be the best match for your tonearm (effective mass) to stay in desired resonance range from 8 to 15 hz

The formula noted by Chakster is correct but it has a very limited purpose, viz., assuring that a particular cartridge/arm combination resonates somewhere around 8-15Hz. A resonance frequency in this range is presumed to avoid excitation by either musical signals cut in the grooves or typical record warps.

The Shelter/Rega combo falls inside this safe range, as do probably 90% of all cartridge/arm combinations. No need to fuss any further about the math, it won't tell you anything more and certainly won't predict the sonic behavior of any cartridge/tonearm combination. For that there is only one test, the ears of the listener.

As I originally posted and Stringreen repeated, what sonic issues (if any) are you trying to address?

>>The 103R is similar in compliance to the Shelter...

Actually, no. The compliance for the Shelter 501 MkII is 9 x 10-6 cm/dyne, while the compliance for the Denon DL-103 is 5 x 10-6 cm/dyne. That's quite a difference. There are very few if any, modern cartridges with lower compliance than the DL-103 family, which makes them a difficult challenge for use with most light, short tonearms (like the RB-250.

Resonance compliance is a complicated subject- it's not just about cartridge/tonearm weight or damping. Adding a heavier counterweight or mass to the headshell will not make a DL-103 sing on an RB-250 arm.

The Shelter should work with the RB-250, although as Stringreen mentioned you will need some method to adjust VTF, and you have few good options for azimuth adjustment, which is critical in order to achieve best sound with any MC cartridge.