Please do post pictures. There is no reason why you can’t use the 72 MHz stuff. There are lithium based batteries available. The LiFe 6.6V batteries will be best for your application if the servos can handle the additional voltage. Some Futaba servos can’t handle more then 5.5V. Any of the 3xxx series are junk IMO and can’t be run on anything higher then 5.5V. The choice there would be to replace the servos or use a voltage regulator if you go with LiFe batteries. You will also need to buy an appropriate charger. The engine is of interest to me. I did not expect a twin as until fairly recently they weren’t many available under 70cc. Perhaps you could let me know what size prop it has, that will tell me the size of the engine.