YES the RB26's have a shim under bucket set up sort of like Supras.
The RB20 as well as the 25DET has solid lifters.
THE VG30's lifters are NOT interchangeable, the 25's are reasonably larger in diameter. I had a problem with my lifters, ran the motor for a while. Took of the valve covers, etc, Remove the cams. Take out the lifters, soak them in Oil. Put them back in. Are they ticking, could be lack of oil ?
What is the problem with your lifters ?