The spikes you now have are PE 240-725.
They are threaded 1/4"x20.
The 240-730 is threaded 3/8"x18. To use these, you will need to remove the threaded inserts, redrill the holes to 1/2" and sue the new threaded inserts.
You might consider something like the 240-718:

I think that these also use a 1/4"x20 thread, so you can use the present inserts. Because of the design of the plinth, you must use threaded inserts rather than T-nuts. So, you will have to check the thread size.
Bob