The 103R will work with an RB300, but the effective mass of the arm is a bit lower than would be best for the 103R. None of the heavy counterweights will solve this problem. The DL103D is discontinued, and you probably will not easily find one of those.
The way that alot of Audiogoners have overcome this problem, is with the DIY HiFi tonearm mod. It matches the Rega and OL arms to the low compliance cartridges quite well, is cheap, and easy to make and install.
The way that alot of Audiogoners have overcome this problem, is with the DIY HiFi tonearm mod. It matches the Rega and OL arms to the low compliance cartridges quite well, is cheap, and easy to make and install.