I don't know if this thing is for sale or not but I would guess that it would take more work than this old thing is worth to convert it. Most of these type buses seldom make it past 20 years in their prescribed service anyway.
http://chicagoareafire.com/blog/2019/11/former-chicago-fd-comm-van/comment-page-1/#comment-738473
Being a 90s Ford from Chicago, I can only imagine the horrors lurking in that thing's undercarriage. I'd hesitate to take it if it was free.
How many miles are on this vehicle? It might have spent a lot of time sitting around. I once bought a 1955 REO truck that was government surplus with 9,000 miles after 45 years of "use". It was solid and fully functional.