ISO-specific type of receiver set, which Idk if even exists.

[DeauxJoe]

Seems like builders' kits are getting harder to come by in general, so I'm assuming this is a long shot. But I am curious, does anyone make matching small and large frame billet receiver sets with monolithic uppers and handguards with integral Arca rails?

 

[N_Turs]

Almost, Jp does everything you asked with the exception of the integral Arca rail. Ridgle line is the only one offering that in a semi mono upper currently. There has also been talk of them doing a large frame which Im sure they will eventually.