I have had several sets of small pattern axles drilled and tapped for the larger(4.5 on 5) bolt patterns several times
We used the Moroso or Mr Gasket 3x1/2x20 screw in studs, make sure and spot weld them on the back sides of the axles also
Have the same machine shop drill the stock brake drums for the large bolt pattern also
If you want after market axles you can have them custom made for the stock rear brakes and have the stock brake drums center machined out to fit the larger big bolt pattern axles center register, you will also need to have the axle flange diameter cut down to use on the small bolt pattern brake drums, or swith it over to a set of the larger bolt pattern brakes, drums and backing plates with the larger axle spacing between the axle and brake drum spacing