Doing very mild build 351w roller with gt40s. HO mustang cam with 1.7 rr. .479 calculated lift. Ford tech said gt40 springs are not sufficient. Suggested 110 lb closed pressure. 265 open for this application or thereabouts, Found some springs that match those ratings almost exactly. Known quality brand. This is only about 20% more than stock but is this too much pressure for stock retainers? Not a screamer, maybe an occasional 6k rpm. If not, Alex's stuff known to be American made, or at least quality?