I was looking at it more from a view of if you are going to buy a skyline you are better off buying a Turbo one as buying an NA one is like buying chinese knock off nike's...they look the goods but it's just not the same. Best bet is to save the coin and drive something else until the right car comes along and then go enjoy it.
Better bang for buck out of a turbo model, 2.5l 6cyl non turbo is not exactly an efficient piece of technology to move something the weight of an R33 and doing upgrades to it is just throwing money in a hole.