Ths STS D28M takes standard glow plugs. If the OS #8 is a standard plug (not a turbo plug), it will fit on the D28M. I'm not sure, but if an OS plug has a letter "p" in front of the number (example: P4, P5, P6), then I think they are turbo plugs.

Try to buy one each of a hot, medium, and cold standard plugs so you can advance or retard the D28M's timing according to outside conditions. You can then tune the needles normally for performance.

I'm not sure what rating the OS #8 plug is; you can search on-line at OS's web site to find out what type of plug it is.