Hi ANAND:
Just as you said, the easiest way to use K66 with MQX is MQX v5.
Please refer to below link
MQX™ v5 Software Solutions | NXP
Porting to K66 is recommended to an experienced user. You can refer to the document MQX_BSP_Porting_Example_User_Guide.pdf and MQX_BSP_Porting_Guide.pdf.
It is not an easy job, you can start with MQX 4.2.0 with TWR-K65, since K66 is similar to K65.
Regards
Daniel