I can remember when my dad worked at a gas & electric company in our hometown,they had a huge fleet of trucks,everything from C-10's to C60's ,a few 4x4 3/4 tons too,all ranging from the late 50's to early 70's vintage--and almost 50 "company cars" employees like him drove most of the time that were used to go up to 100 miles a day checking gas pressures at LNG plants ..
The company stuck with straight sixes well into the late 60's--they liked Dodge Dart wagons with the slant six a lot,they used those exclusively for a decade or more,just because the engines rarely gave any troubles..in the late 60's ,they decided to add a few V8's to the fleet,one was a '68 Chevelle wagon that had a 307 and a Powerglide..
Mostly they had GM trucks,not Dodge's,I guess because a local GMC truck dealer gave them good discounts on fleet trucks and would service them until out of warranty..
That 307 engine smoked from day one,and after 32,000 miles the fleet mechanic decided it was never going to "break in" and he re-ringed it with cast iron rings,he claimed chrome rings were not good....it ran sweet thereafter,and my dad liked the car so much he bought it from the company once it hit the mileage and age they usually got rid of them--they used to give employees first dibs..he had that car a long time..I got my license in it,and used it often until I got my own vehicles .
I wish now I had tried to buy some of those fleet trucks,nearly all had 292's or 250 sixes with manual transmissions-mostly 4 speeds..they often sold cheap for like $500 too,and they were kept garaged and well maintained..they probably had at least 40 GM trucks from 1960-66 vintage and several 67-72 models back then up for grabs..
The C-60 bucket trucks even had 292's except for a few 50's models that had the GMC 302 straight six or a 261,they also had a mid 60's C-60 with a 409 V8,and the company ordered a "spare long block" for it in case it ever blew the engine--they never used it,I recall my older brother trying to get hold of it when they were auctioning off a lot of "obsolete" equipment,but he didn't end up with it..it was still bolted to the pallet it was shipped on,all covered with cosmoline and shrink wrap..bet whoever scored that was happy..