fitting roll over bar

can anyone suggest how to accurately enlarge the holes in the capping on my 90 so as to accomodate the larger bore of the feet of the military roll over bar...??? The present holes are for the galvanised hoops, about 1" diameter, and I need to enlarge to 2" diameter. Thanks.

The way I go about enlarging holes is cut a hard piece of wood to go under the existing hole and beyond the intended hole size, clamp this with "g" clamps to the panel and then drill with a "Starret" hole cutter. This gives a solid surface for the pilot drill of the Starret cutter so allowing a neat hole to be drilled/cut. Starret hole cutters are available from any good hardware store, do not buy the cheap and nasties from B&Q etc as they will only be any good for 1 hole and then fit for the bin. The arbour and pilot drill cost roughly £9/10 and the 2" hole cutter £7, when using the arbour with the hole cutter do not use the locating pins as the "stop" but tighten the hole cutter all the way on the arbour as it then gives a better cut, use a slow speed drill nothing above 500 revs and use plenty of wd40 as a lubricant. I use mine to cut through 4mm steel and 8mm Alloy with no problems and only have to replace the cutter every 6 months.

Stig, Thanks for a speedy reply. That is the best suggestion I've had so far and sounds like a plan....I'll be giving it a try this week. Cheers.