I've had issues with the bolt in 12 litre ones that I sell when fitting to S2. The small cups that hold the bottom tank rubber need removing or bending flat for enough clearance to get the tank in. Not sure if that would apply to this tank also and not sure if the Spanish frame has the same tank rubber cups.
Just try it, it'll either fit or it won't. If there's enough clearance then they're a doddle to bolt in. Much easier than the 12 litre ones, as getting the tool box back in is difficult as there's very little room to get at the trunnions that hold the tool box in place.
i have a 13ltr one fitted with a ts but it doesn't give much clearance around the carb and tool box i much prefer the diablo or the oiltek ones with a legsheild toolbox
Thanks for the info, I'll give it a go and set aside plenty of time for fettling. Also going to treat myself to a rear exit fast flow tap at the same time. Thanks again.