the website you want is
www.discounthydraulichose.com
on the right side of the page,under fittings and adapters.
click on british and metric.
click on part #9605
there will be a bunch of parts listed.
the part # you want is 9605-04-08x1.25
this is a 8x1.25 straight thread adapter with a male #4 jic on the opposite end. you can then adapt the #4 jic to anything. jic a standardized fitting in the hydraulics world and they make millions of adapters to get you connected to almost anything like pipe threads, bsp, bspp, compression, you name it
also dont forget to order a few of part # 9500-08mm
these are the sealing washers you will be using to seal the metric adapter to the enging port.
i would suggest using these over the (honda) aluminum crush style washers only because they actually fit the 9605 metric fitting better.
use the crush washers under the bolt heads when you finish and reassemble the plugs.
hope this helps