If you have standard bars it should be cake. The sportster is a very easy bike to ride and very agile even at slow speed. If I could CHOOSE any bike, a sportster would be on the short list and maybe even at the top.
NJ asks the damn near impossible on the road test IMO. Need a wheel base like a ...... unicycle! most guys rent peds
Actually as of this year if you use a moped or anything under 500cc you get a license for a 500cc bike or under. I only know because I took the test with a friend of mine on 1/2/13 and after renting a moped for the test we were told the law had change that day and the test was to be done on a full size bike.
Testing for CC specific classification used to be standard in a lot of states. A bunch got rid of it and I never understood why. I had to get a 250 class license first, then it's anything g goes above that.
The only issue I could see with a 48 is it has a very low lean angle clearance which will make the turns less forgiving for correction.