No mods needed to fit on my R34 GTR but I have a M-Spec and they come with the bigger battery . On none M-specs you need a wider top bracket ( 7" instead of your standard 5"), there is another hole there to fit the wider bracket, cables should reach, your battery tray will be 5" so if you want to replace it you need a 7" but its a sealed battery, most people don't use the tray.
To replace the battery in the 34 R you need to remove the steel backing and undo one side of the strut brace.
They have a one year replacement warranty but you have to send it back to me, never had any back so far .
Owgasm,
They are different, as far as I know they ( supercharge gold) are calcium positive plates and a mixture of calcium and lkead negative plates, correct me if I'm wrong. I'm not aware of the specs on the 36 series mate . I don't know what kind of 34 you have but if they fit on standard 34 R's they must be smaller than these ( 5" same as the stock battery) . Some normal 34 R's have the bigger battery as an option ( winter option) All UK spec cars have it as well.