I think the 'BT4' is legal. The T4 has a 288 mm wheel base.
These are the 1/10 buggy rules page 56 from the ROAR rulebook:
Length (B) Maximum 457.2 mm
Width Maximum 250 mm
Height Maximum 203.2 mm
Wheelbase (A) Maximum 292 mm Minimum 229 mm
If you are like me and really struggle with 1/10 buggy the longer wheelbase can help but if you are fast with with the standard wheelbase, it will probably only slow you down.