Did you also have the target hammer and trigger changed to service type? My 4” 24-3 I bought new in 1983 has the service hammer and trigger like every other 4 incher I’ve seen. My 6 1/2” 24-3 has the target hammer and trigger and I thought they were all that way. I think I read here that the 24-3 barrel was actually 4 1/8” to keep 1983 barrels from being faked on older guns. Sure enough mine is that length. Your’s is probably a true 4” if it’s an old one.