65 dart 318/904 swap- tailshaft

Is there any shortcuts I can take instead of finding the correct driveshaft to go into the tailshaft of the 904. For instance maybe does the tailshaft from the original transmission fit the 69 904 tranny. My car had the slant six before the swap.

Its got a 7.25 rear. Is the 318 gona fry it. Should I just save all the hassle and go with a 8.75 rear? This decision could solve my driveshaft issue.