backdate 76 GC heads to 73-74 GA or GB heads Options

[SuperDave]

I'm a newbie here. I've tried searching pelican and here to no avail. My apologies if this has been covered before...
I am very close to buying a 76 2.0 to replace the 1.7 in my 72. The 2.0 still has the original heads and emissions equipment. I've read enough to know the emissions equipment made the car run hotter and less efficiently and my state (Oklahoma) doesn't require it so I'm planning on removing the air injection.
Three questions:
Are 73-74 heads a bolt-on for the GC engine?
If so, would I gain anything by replacing my 76 heads with GA/GB heads or should I just fill in the holes like was discussed in a recent thread?
I've heard the valve sizes are different between 73-74 and 75-76 heads, but haven't been able to verify this. True or false?
Thanks!
David

[type47]

Breather ports are little pipes that allow relief of air pressure formed in the crankcase to escape and be put into the intake system. On the upper side of the head, but off to the side will be a "boss" which is a little raised area through which a hole can be drilled and a pipe located. Hoses are then attached to the pipes and routed to a collection junction (anti-flashback valve, a little 3-way connector) then to the air cleaner assembly to be burned with combustion gases. Actually, I didn't know that GC heads did not have the pipes (among the many things I don't know). If your heads do not have the pipes, I suppose you'd have to remove the heads to install them (would require dropping the engine). To replace the emissions injectors with plugs should not require engine removal. Awkward, but it should be able to be done with engine in.