http://www.y-blocksforever.com/tech/html/c4conv.html
http://www.ford-y-block.com/c4install-car.htmthe above may be useful. 
one point, you are required to tig weld the converter studs, they move   so check flex plate fit preferably out of the vehicle  .
 
stuey

Ok so we got the C4,  and I am ready to get the parts in order to stuff that baby in the 56,  question has anyone mated a C4 to a stock , Y block in a truck , I'd like to know about how much effect the automatic transmission effects the performs ..  when it hard the 3 on the tree it moved pretty good.. At some point someone must of rebuilt it ..  this truck needs to get out on the road its been in my garage for 6 years , it does run great by the way.. I'm looking forward to this I'll have my part by end of the month ... hoping Sept ..to get it out .. thanks!