Besides the above caveats, re: proper-sized centered holes drilled 90 degrees to the stock bottom line, generally sling swivel posts are installed approx 2" from either end of the wood end of the stock.
That means no measuring from the end of the buttplate/recoil pad or the end of a contrasting forend tip.
The buttstock stud on a solid wood stock is a wood screw design.
The same type can be used on the forend, specially a beefy one - but on a thinner one, you'd be better off with the other type of front stud, which is a machine screw design with a nut that goes into a recess you cut in the barrel channel for barrel clearance. This type comes extra long, and is shortened for each particular installation.
The machine screw type can be use for both front & rear on hollow (synthetic) stocks, with the use of a backer inside.