Finished
was really struggling with the 2 smaller clamped hoses above the overflow until I read another post on this forum, I'd been trying to get the big rubber wiring grommet to come out into the boot with no avail, then I read that it just pops inwards when pushed, before this none of my tools could get the clamps close enough to the firewall to provide a good seal, almost called a mechanic friend for help, then discovered this and was finished in 2 mins with some 90 degree pliers, another top tip is to attach the oil filler neck to the tank before inserting through the firewall, I did this as I needed to replace but now realise taking the old tank out would have been infinitely easier if I'd have left the firewall end clamp alone and undone at the engine end, live and learn I guess, hope this helps others in a similar situation, as stated the furthest I'd gone into a car apart from filling with petrol before was changing a wheel, now I'm ordering tools and parts to do my own oil and filter change to see what state IMS bearing is in, hopefully fine but if not this will be a DIY job also, the joys of a porsche on a budget
Apologies to whomever on here recommended the the wiring grommet, I'd give credit but I've read that many posts it could be anywhere