If you do put in a 700r4 make sure it is a 1984 or newer. They started making them in 1982. From 84 on they were beffed up with a larger output shaft. I had one from 82 in a 70 monte carlo and I never liked the way it shifted. They have a throttle valve cabel that is very important to have adjusted properly and there is a special linkage depending on what carburetor you have you can't beat a TH350 or TH400. That's my opinion.
On my 70 monte the engine had a high performance camshaft that took to much vacuum. I had to install a rotory vane vacuum pump. Machined a plate to mount the pump to the frame and wired it to the ignition. It worked great. This was the car that the inspector lied about road testing the car. I had so many problems with that car I had to get rid of it. I found a Really nice 71 monte close to home. I bought it and transferred all the best best parts from the 70 before I sold it.
I agree not lifting the engine by the harmonic balancer . Put wood as large as you can under the oil pan. another thing I will add, if you rebuild or put in a new engine, always put in a New harmonic balancer.
I know the difference between the 70 - 72 grill emblems. But would one from 72 with the lines bolt on my 71. I happen to have found one for a a very good price
I'm sure not everyone will agree with what I did. I'm not a numbers matching guy. I have certain things modified. For the hood springs I put a smaller spring in the ID of the hood springs. Works good for me.