Any things better...
Any newer motor will wake that monte up. I've had many different motors in my monte carlo. My 1980 monte was original with v-6 turbo. someone pulled that and put a 327 in it before I bought it. Then had a 350 junkyard in her. Blew that. rod snapped and blew the cam into 3 pieces. She sat for a bit. and now I have have a 283 under the hood.
Since I've had the car I've been through 3 rear-ends, stock ones, .243s somewhere in the low rang gearing ( now there is a 10 bolt posi .410 back there) even the small 283 moves with those gears.
Transmissions are cheap, the stock ones at least. I think I've ruined 4 automatics, down shifting alot. I do have a reconditioned trans in it now, built by a trans guy. No problems now.
This was my first car. And I did all the swap outs my self. Since I was 15 or so. I'm now 27. I still have fun just trying new parts out even though every thing is just about the way I want it now. It takes longer when you don't have the best information on what works the best and a low budget.
So you will be as satisfied in doing something the wrong way as this will teach you a lesson that you will learn from. And trying to push stock parts past there limits has its own ups and downs. The one junk yard motor proved to be a strong one. I had that thing screaming everytime i went out. no lie 6400,6500 rpm range chirping second!!! all of the time!!! This is the one that finally broke the cam into 3. It was a blast. I spent $450 on that motor. I do have a bit more money and time spent on the 283 60 over motor in it now.
Have fun with it. Since this it the first build, just get that motor under the hood and go with it. You can always pull parts and change things with the motor in the car. You may find that the thing drives great without doing much to it. and on another note the rear could be your weakest link. The low gears may make the take off a bit sluggish. If you were to hit a swap meet and find a 7.5' posi unit and a set of .342s , 355s, 373s, you would be burning rubber all day. Also you could search for a exact match g-body gm drum to drum .342 posi rear out of ss monte , regal , cutlas, grand am or olds and do the swap in a day or less. I did a similar swap in the parking lot at my old town home in the rain. I had the day off and was determined.
Sorry to write so much. I love monte carlos. I've had four. There are plenty of aftermarket parts for the 81-88 montes. Almost any body or interior parts.
Tell us a bit more about the car. It may help if we could understand what plans you have with the car.