Treemover6

My family has had a tree moving business for 40+ years now and one of the trucks we use is a 1984 (I believe) Mack Series R with an 80" Vermeer tree spade on it. Any insight into this truck would be appreciated as it appears Mack made every combination of truck they could lol. It's got a 5 speed with a standard/lo/reverse stick and I believe it's a straight 6 motor. (Will add more pictures when I can). One thing that is interesting about it is I've heard from many people that your not supposed to split gears with the right stick, but my family has been doing it for 40+ years on the original transmission so it must be pretty tough. Thank you.