Engine Replacement

[tomschauer]

It seems everyone is trying to discourage you with this. I will not be too far off.
As mentioned, first, be sure the stringers are good. This vintage had wood stringers, I had one.
The 454 will fit, but will have different mounting points, so you will need to at least move the motor mounting plates, most likely replace them.
I am not certain, but I thought the big blocks had a different diameter flex plate and outdrive attachment diameter. You will want to verify. The alpha 1 gen one I believe had a 300 max HP rating, so you will be pushing it a bit. I do know they did use these drives with 350 mags and 454's on factory boats, so it's not out of the question. If you move to the bravo, you will need the complete gimble housing and I think a different cutout in your transom.
Just make sure you know what you are getting into before you start.

[paulr]

The Alpha drives couldn't handle my twin 6 cylinder Sea Ray years ago. I could imagine what would happen with a 320 HP 7.4L big block.

[bud37]

I just think the op asked for advice and he got some honest well considered/experienced advice as to how to proceed is all. Lots of bits of info that perhaps would have been missed until too late IMO.