Welcome to the Stovebolt! You've got quite a project cut out for yourself. You're right, you will need some help.

No 454, or any other big block, fits. Small blocks will fit, especially if your truck came with a 283. If not, get the motor and tranny mounts from one that did, and go that route.

Stuffing a big-block in means a lot more welding and fabricating and parts-fitting, etc. - and $$$, too. Figure on serious money. The big-blocks are also much heavier, which won't help handling much.

I'd suggest stuffing in a serious small-block. You'll wind up with more performance with a good small block, than a hacked-and wedged BB.

Good luck!
George