Mugen conversion

I have a Mugen MBX 5-R buggy that I want to convert to electric.
Can anyone give me some advice which NEU engine I shall use in my Mugen?
The ESC will be Castle C. Mamba Monster V3/MAX, no doubt about that!
I think I will choose an engine from NEU 1500-series, but I don’t know which….. what shall I look for? I want to have a long driving-time at the track and I want to beat the nitrocars
I’ll be using a li-po (from PolyQuest) with 6S and 4500-6000 mAh, well’see..
The Mugen MBX 5-R has a gear ratio 11.79:1, if that is some help…