do 2 4 inch ports, each or them 11 inches long and you should be around 32hz. you could do this modification in an hour or so. if you can fit the length, do 3 4 inch ports, each of them 18 inches long. that would also be tuned to 32hz. 2 aero's would work, but i'd try to get at least 3 of them in that box. 2 6 inch ports would be 27.5 inches apiece long to get 32 hz. you can kinda take your pick. 2 6 inch ports would work best i think. so your choices are as follows
2 4 inch ports, each 11 inches long - 32hz
3 4 inch ports, each 18 inches long - 32hz
2 6 inch ports, each 27.5 inches long - 32hz
whichever one you can fit.