Been across this before a few times , and the reason for that change is vapor lock , they installed a insolator spacer between the block and pump to bleed off some heat , most of the newer cars had A/C in them and running hotter for the smog crap that was put on the engines , fist time I came across this was at the ford dealer I was working at I changed an engine out with a reman engine , think it was fread jones that was doing all of ford rebuilding back then , that took some time to figure out because I used to old pump because the cust said he just changed it , just the beging of the problem but the parts guy found the diffrence in the parts book , next one was when I brought a 73 wagon with a dead engine , most I the time have seen electric fuel pumps installed because of that trap that was built in , good find and 'sure we will not hear the last of it ,