My 3 powerplus chassis come off 1 1978 build engine, 1 had an engine swap so I don't know the year and the most recent one I picked up is also 78.
Out of the 3 I have, like the super start Mustangs, I will only be able to make 1 good one because only 1 of the 3 bases are good enough to use, now the powerplus base is a different cast and, to speculate only, to save on weight maybe the walls aren't as thick? I really don't know?
I do know that any of my high arch mowers from 1971 though to 1977 have very little issues with the bases except for 2 and they were a 1973 Red VC-SPORT and the first Victa that started all of this for me my 1975 Green VC-SPORT. The reason that these 2 bases were in poor condition is because I got them very very locally and I live 3 minutes drive from the beach one way and 4 minutes the other way. Most of the soil here is heavy with sand and all of the damage to these looks like sand blasting. Every other hi-arch from 71-77 are pretty good.
The first evidence of poorer quality decks in the 70's that I see starts with the Powerplus and some of the store brand decks from the end of the 70's and early 80's and then definitely show serious deficiencies in the Super Start Side pull Mustangs.
Then the amount of the 86 White Mustang and Yellow Vortex bases that I have seen with massive cracks or chunks of the bases is very high. Those bases appear it be thicker and they definitely are designed to take the abuse on the front, I guess that's been a problem that they wanted resolved for a long time, and in doing so they have gone for a durable but lightweight alloy to thicken things up and really fix the issue with the front breaking. But in doing this to the design or the choice of alloy when a big rock is thrown at the side wall hard the design has been made to reinforced the front of the base and isn't equipped to take that kind of hit on the sides or the alloy has issues with taking the impact of high velocity projectiles but great for low velocity impacts and thus protecting the front from breaking when bashed into a tree.
This is all speculation but is speculation based on my own observations that I completely admit hasn't been over a long period of time.
