I changed them on my R180 and R200. Just like a regular crank/cam seal though with the shafts out you can lever them quite easily with a screwdriver or ideally a seal remover tool. Installation is normal too - either hammer with an even block matching diameter pipe or slowly with a punch.
I can't remember if the seals I used had the flare on them last time. Usually if you don't buy the Nissan ones a regular seal shop will have the right one without the extra flare to reduce dust. If it's strictly a tar car I think you could get away with it.
910 S3 Bluebird - FJ20ET, E85, IRS, 5 Speed, 4.4 LSD
910 S3 TRX - RB25DET, Coilovers, S13 Front end, Power Steering
RA23 Celica - 18RG, Twin 40mm Webers, Coilovers, rolling on SSR mesh 15x7 0s.
1600s arent the only datsun