heck you just have to get creative..... used to have the starter block off an 8100 on  a 4020.....



Deere has had a pretty standard bolt pattern for a long time..... I think it's  narrow or wide, and if you have the right starter block it may have both.  Worse case--- you drill 2 holes.....


Or for a few extra weights, put a longer length of ready rod in, and just keep adding slabs.  If you're solo, you may have to spin a nut on each one.......... basically letting them overhang the block(probaly not a reccommended practice....but works in a pinch)