Changing intakes

I found me a 64,65 2x4 intake for a 273 and was wondering how hard it would be to re-do the bolt holes to make it fit a 66 273,I know they are smaller and different angle i have read where you just drill them out to fit the bigger bolts is that right or what do you have to do.I can get it cheap and i like the looks of them.It's not a tunnel ram just a flat intake but it's in good shape.Thank's for any help.....