For those of you looking to change the blocks on your running rigging, look at Lewmar's synchro blocks. They're stronger than Harken, equal in strength with Ronstan and Schafer, and between 1/2 to 2/3 the price. West Marine carries a selection and can special order what is not normally stocked, or you can try Lewmar directly. I changed the hardware for my main and jib sheets and am very pleased.
Thanks, Dan. Was looking at my '79 OEM blocks yesterday, thinking this is a thing I'd like to change/upgrade before long...