Replacements are not necessarily the best option 'these days'.
Even back in the early nineties when I was playing with my MGBV8, some replacement pumps were below standard in the impellor department. Some impellors were smaller diameter than original, and had increased clearance between the impellor and body of the pump. Also the shape and alignment of the water channels were not exactly as they should be. I kept my original pump for years, just in case.