Hi John....since I am familiar with your tank
thought I would let you know how I will be doing it
Mark out holes as per sender/rubber gasket then using a suitable tap that suits whatever bolts you wish to use ...eg 5mm hole for 6mm tap then take your bolts
(I'm going to use stainless) and do one of two things you can either cut a slot in the thread end of the bolt to accept a screwdriver or file two flats to be gripped by a mole wrench or adjustable spanner.....now with a dab of blue holymar (petrol resistant) on the underside of the bolt head, proceed to screw the bolts up from the INSIDE of the tank to a LITTLE past hand tight. Now when you come to mount the sender use either the screwdriver or a set of mole grips depending on how you prepped the the bolt ends (after you have put a nut on of course) to hold the bolt while you nip up the nuts they do not have to be very tight to give a good seal......job done
