Big block toploaders are not cheap.
You can get a used one off of ebay and have it rebuilt locally to save a bit over the David Key.
http://cgi.ebay.com/ebaymotors/FORD-TOPLOADER-4-SPEED-68-GALAXIE-390_W0QQcmdZViewItemQQcategoryZ34208QQihZ010QQitemZ200080411458QQrdZ1QQsspagenameZWDVW
Here is...