454 in a 63??????

[undeadchevy]

I have a !963 long bed, bagged in four corners, it has the origional 283 in it now and i have been thinking about swapping it for a 454. my main concern is will the motor fit with the heater box still in it and what kind of mounts should I use? For some insight on the frame it has been cut and Zed 3inches in the front and boxed about 6incehs past each ther places were I cut and rewelded everything. im not for sure I want to go this route yet but just looking for some info to help me make up my mind. I'm only thinking about doing this becasue i have the oppurtunity to trade some junk for a low mileage 454 and the 283 thats in it now doesnt have any compression on cylinder 2 and I want to gert away from the 283 because no matter what i do performance wise it's still a 283. so any help here would be great.