It has been a year since I installed mine, but...I don't think the hole size is much different. Make sure you find the sockets before you pound/drill...just so you get the hole just right...I seem to recall I just drilled em out.
As far as 6 V bulbs go, not sure if you have Checker Auto Parts in MI...I don't buy much there, but they had the best supply of 6V bulbs of every size in my area.
