reducing exterior door opening

[417welly]

Hi all
I'm looking to fit some external composite doors + frames
The external openings seem to be unusual sizes (period property)
I'm having difficulty sourcing exact sizes within my budget so looking for advice on how / if to fit frames that are smaller than the structural openings
I have my eye on doors / frames around 1 inch either side narrower than the openings
Wondering if pre lining the door in some way and covering join with trim is the way to go. Maybe use super thick shims and filling void with foam would work. or maybe there is a better solutions?

Cheers

 

[Wayners]

Not my area but framer extenders to pack the door frame. Ask suppliers. They just clip on to make frame wider