The conversions to mid 9:30s and 4:20s are about right.
It didn't just happen overnight, but he probably transformed pretty quickly once he got into their system.
I think he went to jr. college (maybe Metro State in Denver) for a year--before going to Adams. Is that right?
The story goes that he didn't train a lick, or hardly, the summer before going ASU, and arrived at campus out of shape. They had a 10 mile time trial the first day and he "about died."
I do recall seeing his name in the early 80s, primarily as a miler (sub 4:10 indoors and at or near the top of DII) and 5000 runner. He won some DII championships but was relatively unknown outside of Colorado until (I think) the 1984 Olympic Trials.
Rick Robirds was another one, who was even slower in high school. He went to Sterling, CO (elev 3000 something) in the mid 80s and had PRs like 4:50 and 10:10. By the end of summer before college he was running sub 16 for 5k on the roads (I remember getting outkicked by him at one race) at 5000'. He went on to win some DII championships and was a 28:20 or a little faster in the 10000.
Vigil developed dozens of runners from obscurity to become really good.