It's a Cox Conquest .15. Now called the RJL .15.
It's one of my alltime favorite engines. It should turn 25k plus with the competition head and minipipe. (6 5/8x3 or 7x3 prop. This isn't your garden variety .15, it has more power than most .25's. It's rated for upto 70% nitro. You can probably find an RC carb for it at Mecoa as they still have some parts.

Wish it had been me that got it.

Foamguy