Combining the Ampere of two voltage regulator?

Using Arduino General Electronics
4

Well the following are 12vdc 3 amp linear regulators in TO-3 package:
78H12
NTE933

and lambda sometime ago use to have a 12vdc 5 amp regulator in a TO-3 package that you can sometimes find sold as new old stock:

http://www.ebay.com/itm/LAMBDA-LAS1912-12-VOLT-5-AMP-TO-3-REGULATOR-NOS-78H12-NTE933-EQUIVALENT-/380547135339?pt=LH_DefaultDomain_0&hash=item589a60776b

Lefty