will fuel tank placement, size and shape be something we can specify/adjust in game?
Nope, that’ll be fixed on the basis of chassis etc.
rats… but understandable i suppose… oh well… can’t have it all
so if you make a car with a MR or RR layout, the fuel tank would be located where? i know from my old 2nd gen MR2, it was located under the rear trunk, but in my personal opinion, they’ve should had placed it more in front of the car, with car balancing in mind, even tho they did manage close to 50/50 with the tank where it was. but in winter season i’d really prefer more weight on the front wheels. however i do know Porche (i think, correct me if i’m wrong) did have a front mounted fueltank on some of their older models. this said, i think it would be a viable option to give the fueltank a optional placement, like a “front, mid, rear” option ticker, with handling and car behavior in mind. tho i’m not a programmer, so it’s up to you guys, keep up the good work 
Most modern cars have the tank just infront of the rear axle for safety reasons.
Yeah, we have to pick the design choices that have the most relevance, gameplay value and impact on the overall design of the car. By those measures its not a valuable choice compared to other things we could put the effort into
Mercedes Benz placed the fuel tank behind back seat for safety reasons on a lot of sedans in mid 90’s, no idea about the more modern ones
Unless you want to make a ford pinto it shouldn’t really matter