If you go into the gas engine forum, a sub forum in Giant Scale you will find pages of people using the same engine. There you will see what ignition packs most people are using. I do use Lipo packs in my electric powered planes but as yet I am still using nim for my other aircraft as flight packs. Because of that I would use two 6 volt nimh packs with two switches. My last giant scale gasser I used three packs and three switches and all batteries were the same. I also used the packs as weight to achieve the CG. All three had to be placed forward. There are a lot of choices of battery type these days and each has it's good and bad points. Just a choice thing these days and your instructions with the engine will tell you what they recommend.