The list to modding leaf spring suspension is endless, so it depends on what you want, if its just a bit of height then yer, longer shackles, but then too long and you need to lower the spring hangers, also all the pipe lines to the axles, if you keep going with mods - the prop shaft, dampers, you can get revolver shackles and it goes on. Your tyres are about as big as you can roughly go as standard, you will need either spacers or alloys with a good offset for bigger fitments, choose alloys not spacers, 255/75/15 will fit fine, if you do a body lift you can fit 32" tyres with about 11.5" width on 15" rims - but dont fit these unless you have lifted it or youll be sorting out bits of body work,There is alot of stuff on this forum about modifications and pictures, i suggest you have a good read up on modding before doing it.