That's the wrong one Neil. The GEMS trucks use the multi-function fuel pump/fuel injection relay. The one you posted is for a Lucas truck. World-Pac shouldn't be used as one's only reference, LOL, my wife's employer has just recently taken over their catalogging, give her some time to get it fixed!
P/N YWB100820L $60 bucks is a bargain.
That said, if you're familiar with RRL, you can bust open the box and replace the relays inside with ice cube relays, but be aware that sometimes, the coils have diodes in series with the windings. Lack of the diode will reuslt in battery going flat overnight-very common in Lucas trucks if the worng relay is used.