I've tried to model this part to recreate and revise the drawing several times but all of my attempts have failed.

This is a casting so precision does not have to be perfect.  You might notice that the drawing of the transitions are not shown correctly and the dimensions used don't really fit.

Even with making up my own dimensions I'm having a difficult time making a model anywhere close to the part.

I've tried a few surface tools which I don't use much but I can't get them to form a solid.

Any ideas how I should approch this model?