chambered a 1911 (Used a 38 super barrel mached to fit a 45 acp slide, reamed and head spaced) in that round it is a hoot deadly accurate when loaded to 38 spl wadcutter levels.
Would be a super easy build as no gas operation required Blow Back ...Just a .38 cal barrel blank then have have it turned down and chambered. As it is a blow back no Barrel Extention is required
Are you thinking of Rifle or pistol build??
Use a AR 45 acp Bolt, 45 acp mags (glock), 9mm buffer or lighter such as maybe as light as astandard 5.56 mm buffer could be used.
I would highly suggest a dedicated 45acp AR lower ( just easier)
Now the differance of the 38 Casull vs the 38/45 is the brass Use 308/30-06 etc and a LOT of work for the casull.... the 38/45 clerke is way easier prospect.
you will need the form dies as well as the regular reloading dies to form brass.
If you get deadly serious PM me I Probably can assist on where a reamer is and a gunsmith, where some formed brass, load data could be located.
What you will find out that is the 45 acp case when necked down to 38/45 clearke has the exact same case capcity as the 38 spl.
As a Retired old Army Fart I be Happy to Help a NY Guardsman out on such a project.
Barrel could be located here in a blank format
https://www.gmriflebarrel.com/bx357-25-38-cal-1-06-od-1-20-twist-turned-bbl-blank/
(and btw most 9mm barrels are actually .357" so actually a ar 9mm barrel could be used, and even If you use a .355" bore it will still work you are doing a Low pressure round the .002" differance is nominal the bullet will go out the barrel without issue.)
maybe this one ??
https://www.rainierarms.com/quarter-circle-10-barrels-9mm/
But if you look around if your desire is a pistol format a Pistol barrel could be located.
That round suppressed would be absoulty deadly quiet the bolt would make all the noise a 148 grain traveling at 600-700 fps think hollywood quiet