W123 85 300D whole lot of shaking going on

[hondab100s]

So I bought this high mileage 300 for cheap, and want to make it a commute vehicle. Somehow, the climate control, cruise, sunroof, dome light, headlights, wipers and odometer works. bad news...excessive amounts of shaking and knocking coming from rear/middle of car only during acceleration forward. this occurs around 5-8 mph then comes back again around 18-25. I have already replaced the flex joints, sway bar links, center support, half shaft axles. The unjoint has no play however there is some binding off center which I figured was normal for an IRS vehicle. Also, when changing from drive to reverse the vehicle moves a lot while on the brake, and often a clunk is heard. Upon some inspecting I noticed the mounts that hold the rear subframe to the car closest to the front are squashed...almost metal to metal. And there are these brackets I am assuming are for keeping these mounts from bottoming out into the unibody that have about a 1inch gap to the bracket. The tires are old and dry rotted, however, I see no alignment wear. I'm not too familiar with MB especially this age, but it looks to me the engine mounts have excessive play. Maybe there are supposed to to make up for the vibration a 5cyl diesel may create. It doesn't appear that the mounts are collapsed enough to begin resonating into the cab/body. So I am really just worried about this knocking/shaking at the mentioned mph...also I can't go over 60 as the shaking begins to return gradually to the point where I am scared to go faster...though this is less important to me as it would be for city driving. Any ideas what to check next before sinking unnecessary money into the problem?- Thankyou in advance!!!