You putting a T-10 four speed in it? A five speed would suit the revvy Q4 better.
A V-8 or V-6 WILL fit in the Rambler without cutting. I have an old late 50's "Speed Mechanics" magazine with an article where a guy stuck a "Corvette V-8" (283) in a 54 Nash Rambler, which is nearly identical under the hood to the 58-63 American (inner fender panels and suspension are unchanged, firewall changed on the 61-63 American). They stuck the stock exhaust manifolds on backwards (switched side to side) and ran the exhaust from the front and under the suspension, I believe. that took care of clearance around the steering column. I take back the "no cutting" -- to get to spark plugs they took the front tires off and cut holes through the inner and outer walls of the engine bay. The holes were just big enough to get a socket through. It was that or pull the engine every time the plugs needed changing. Today that wouldn't be bad with a computer controlled engine and platinum plugs, but in the late 50s? You know, I need to look up that article. The humps may have been trimmed as described below... it's been a while since I looked at it.
I've put an early 2300 Ford in one. Had to cut the hump off on one side (left?) to clear the intake.
The "hump" I'm talking about is the bulge right above the suspension. You can't see the upper A-arm mounts in the photos, but the bulge has a ridge running down the center. It's easily visible in the first photo ramzoom posted showing the original engine in. Look to the left of the oil filter. Just below the ridge you can see the edge of a flange -- that's the top edge of the reinforcement for the suspension mount.
In the third pic you can see the angled front and rear of the bulge. The plate to the left of the air cleaner housing is the serial number plate. It's welded on. Many people trim the bulge all the way back to the edge of the fender, but you really just need to trim it back starting where it kicks out toward the engine and meets the vertical side just above the suspension. Look at the ridge -- it angles toward the engine then kicks out. That's the point I'm referring too. That will gain another 3" or so on each side. We had to cut one of those back to clear the intake on an early 2300 with a carb, which doesn't stick out as far as an EFI intake. Most fours are tall, but some of the EFI intakes stick way out from the engine -- further than trimming the hump will clear.