83 kz440 tank...

I have a 1983 kz440 ltd and I was wanting to put a harley sportster peanut tank on it... THe tank has a tunnel length of 16 3/4 inches and the backbone on the bike is only 16 inches. the tank that I took off is 21 inches in length and I just dont know if the peanut tank will fit. I just hate to order it and it not fit then im stuck with it... if anyone has done this and has some pics or some advice my ears are open... thanks!

Jason

this is the bike and the tank i wanta put on it...