how much do u wanna spend...if money isnt an issue get a mandrel bent 2 inch with one baffled muffler rite at the back of the if possible i no theres not lots of room but if you cant get one in there just put one in the stock spot in front of the diff...i would really be investing in a decent set of extractors eg 4 into 1s that setup with extractors is wat i have sounds very nice indeed but my muffler is a round baffled one squeezed up inbetween the spring hanger and the boot floor sits down a bit lower though but looks good
if u wanna do it cheap a press bent 2 inch with a baffled muffler in stock spot will sound better but without extractors it wont sound as good
reason for the muffler as far back as possible is to reduce the resonese in the pipe (burble that datsuns have)
my extractors are hi-tech they are 4 into 1s flame proofed mine are stainless but can get a steel set the same steel ones retail at around 220
i then chopped mine up and made them tuned length(much better)
dont get straight through or a cannon or just a hot dog type muffler(sound #OOPS#)