> If you can convey 95% of the basic ideas in Python

But you cannot.

Some of the ideas in SICP can nearly be conveyed in Python (like lexical scoping, closures, data types, streams). You'll use built-in language features in Python (classes, generators) instead of implementing the functionality. I think that implementing these things is important if you want to really understand them.

An example, cons, car and cdr from nothing at all:

    (define (cons a b) (lambda (f) (f a b)))
    (define (car p) (p (lambda (a b) a)))
    (define (cdr p) (p (lambda (a b) b)))

You can do this in Python in theory, but you can't throw this into a Python course.

Other ideas, like interpreters, require a lot of effort. Try writing a metacircular interpreter!