This is one of those decisions that only you can make... you need to determine how much originality is right for you within the bounds that it can never be truly original.
I would support doing what Jeff, Mark, Hyde, and I all did (even though Jeff and Mark suggest otherwise
) and go with the period correct 5-bolt block. They are out there, and, as has been said, nobody really wants them much anymore.
The Cobra bell housing is the hot ticket for this set up, but it is big money - $1K plus...
The tranny is a T-10, which are also available, but word is that they are not quite as robust as their replacement the toploader.
What you have is fine if you do not mind that it is less original... but still good.
