kasunsamee

G'day
I'd follow the advice ricster gave, I'm just unsure about TD42 plugs. If you search Bosch part numbers for example it will give GPN338 for TD42 and its derivates but not for RD28.
Also glow system in GQ's RD28 works in the different way so unless you rewire/change the control system I'd be wary of using TD42 glow plugs. RD28 uses ceramic glow plugs and 2 types as well [3 double pole units marked yellow are required per engine (last 3 cylinders) and 3 of the single pole plugs marked blue (Front 3 cylinders)] because of the way they can be operated so putting metal tipped cheaper ones from T42 without modding the controls will burn them quickly. See here ==>
Conversion kit for glow system GQ Y60 RD28
Regards

Be VERY VERY careful taking out the old glow plugs !!! Often there is a carbon build up on the glowing portion of the glow plug that makes it almost impossible to get out. If you wiggle or yank it out too hard you can break off that tip.... then you have major sheeeet !!!
I had one on my TD42 many years back that gave me grief. I sprayed heaps of Q20 ( WD40 ) while relatively gently turning the glow plug. It took ages to get it out, but was still quicker than taking the head off to get the broken off piece of glow plug out.
There may be easier ways, so hopefully someone jumps in and adds a suggestion