Welcome to the forum
Glad you and your brother were not hurt any worse than you were.
As for the 'subframe' as you call it, the front suspensions on the '63-'87 trucks all interchange. Here is a thread that will explain a lot about upgrading the front suspension and brakes
http://67-72chevytrucks.com/vboard/s...d.php?t=367260
As for installing the 4.8 into your '63, that is becoming more and more popular anymore. There is a complete section here on the forum dedicated to LSx swaps.
http://www.67-72chevytrucks.com/vboa...ysprune=&f=206
Just keep in mind that the frames from '63-'87 are basically the same.