The vangaurd or howa 1500 is a great action but there is not near the aftermarket support. The factory barrels also typically have to be ruined when getting off.
ya but if your putting on a custom doesnt really matter if you ruin the factory barrel. theres a guy on gun broker thats always sellin take offs in stainless, the guy builds muzzle loaders out of the howas, anyway these barrel dont have a mark on them so he must have the tools and know what hes doing.
shilen sells pre threaded howa slash weatherby barrels, screw it on and finish the chamber.
if you were to build one theres not much you need to do, bolt, extractor and all need no help, true it up and screw a barrel and good trigger, done.
as far as aftermarket support what do you mean, barrel, stocks and triggers are readily available in the howa