I might not be correct in remembering how the circulating pump mounts in a 6-71 but.... While I can remember it takes a special wrench to get at one or two of the mounting bolts...I believe I recall that it's driven by a 3 pronged 'thingy' which mates to another 3 pronged 'thingy'. so once you drain the system and have the special wrench to remove the virtually inaccessible bolt...it should be a 'no sweat' deal.
I'm not twisting your tail guy...but probably the best thing to do is to either have a good Detroit Wrench replace the pump or get ready for some real grief!
With the transverse engine mounting I can't help but think..."I don't wanna do this"!