Yup..Halo's onto it..the 76 ts250a was the last of the old design (aka TM250) it shares the same mag cover and right side clutch pinion setup as the TM250 and the cases 'will' house TM250 internals if you so deside. You may need to blank off the pushrod hole with a TM blank but it's a straight forward swap. The only thing of any real interest that swaps from the later 78 and on case reed induction type motors are the output shaft (maybe), clutch plates, piston, rings , pin, brg, clips and con rod and lower end bearing etc. The rest you can pretty much say was totally new design.