I went the P30 route on my 49 600 COE. The track width was very close and the wheel centers fit the fenders of the COE. I did have to modify the steering box mount some to clear fenders, and reduced width in the front. Motor mounts were in the right place just offset to the passenger side. There are lots of different lengths available and can be modified if needed.
Get as late as you can find. Better brakes and bushings.

47 GMC COE
64 ELVA MK7
67 MGBGT Special
73 MGB V8