Ok you got me looking
quick interweb search and I find this
Momo has a different part number for the early Datsun aka 240z/260z/280zx, 510, 610. etc basically up to 86 (which is #3503) then for the later stuff aka 240sx/200sx (S13,S14), 300zx non tubro, Pulsar ie 87-90's cars (which is #3508). However I have not found a spline count for these momo hubs/boss kits.
But I did find another listing (locally on trademe) that lists the Skyline R32/33, Pulsar, Sentra 200sx/Silvia S13/S14 on the models it works with and they state a spline cound of 34 on a 16mm shaft.
So I pickup my 260z steering wheel which is off the car and I count 36 spline on maybe 17mm but my guess is 16mm as that is what the nut size looks like. I cound the wheel a few time but keep getting 36..
The hub/boss on trade me is only 29 NZ funny money so not a lot of coin if a punt was taken to see if the s13/14 units do fit - better than dropping over $100 USD for NRG short hub to find out it is wrong.