If the engine is 100% standard, then it should start as well and easily as a 100% standard car ( for a Ford anyway lol )
It should never have needed a huge battery

Swirl tank etc sounds like additional and unnecessary weight. Given your main tank sounds like a custom unit, design it right and there should never be a need for a swirl tank, you could easily save a few kgs there too, as well as some money if it was done in the first place. Although changing afterwards would add cost.