88RRC SWB - antilock brakes?

your truck is an 88 MY. according to land rover, ABS was not offered until model year 1990. if you had abs something would illuminate in the cluster advising of abs, furthermore you would have a buzzing on the left fender area where the abs pump builds pressure.

your rattle may be something else, shock bushings and or front shock towers come to mind, loose or worn suspension bushings as well.

Very correct, the ABS took over 4 years to develop with Wabco. It was a huge safety selling point as it was standard for all 1990 Range Rovers.

Another side note, 1988 had only one model Range Rover. There was no LWB offered in standard production for several more years.

the abs was mostly available to the highly demanding and competitive US market, even the 87 model which was the first LR back on US shores for a while came fully equipped with power doors, windows, auto trans and 3.5 v8.
the later basic model offered very briefly was the hunter edition 3.9 v8, auto trans and all manual. while other world markets did receive non electronic, non abs, diesels and manual variants.
as for ABS is a huge debate, some like it some don't, some wish it had and on off feature and some would like an off road selectable feature.
reasons vary from personal preference to expense of repairs when components fail.

It could be worth pulling the hub drive flanges to make sure the splines aren't rotating under loading when the brakes are applied.

If you consider braking over bumps and lock "for example" a front wheel just as it unloads over a bumpy surface, then the wheel could become stationary and with the transmission still being rotated by the torque from the other wheels, the drive shaft wants to keep the wheel going at the same place as the other three. If the splines are worn then it could produce that noise by slipping round inside the drive flange in that "machinegunney" staccato fashion.

I'd look at the front opposite the driver first, then the driver side front.