your old one may have extra weight from years of dirt drawn in from coolant recovery bottle. I mean besides the brass vs alum/plastic.
Totally understandable, thou I did just that to get our coach rad serviced, and my bronco rad re-cored. 100 mile round trip x2, and $900, would have been more had the 55 Chevy pick up tanks not been beyond saving. Went for because I was afraid the shop owner would retire soon, as it is only the owner and his cousin in the shop now both closing in on 60.
Have radiator shop here in Havasu did the new core on dads 72 Ranchero, was really spendy, but ended up with a nice high efficacy brass core. Turns out this the same family shop I use when I lived here in the 80's, did business with current owners dad. He move the shop to a better location.