Am I going to loose my heater on the 67 when I install the big block? Heater hoses on the firewall are awful close to valve covers on the small block in it now.

 

You'll need to swap out the heater core for a big block style,the big block hose connections are moved towards the fender more.
When I did my '69 I found it easiest to pull the right fender part way off for access,it's a bit of a PITA but doable.
This is a Nova but it's pretty much the same as a Camaro.

 

Or you could bypass the heater core altogether, if you're not into originality or don't drive the car in cold weather.

 

I believe the whole suitcase, and heater core, are different for a BB. IDK if just pulling a SBC heater core and leaving the suitcase will clear the BB

 

You can either use a big block heater core and bracket .And drill the holes for them in your small block suitcase .And even take your small block heater core and flip it around ,There are picture on the net if you just "Google" it.

 

Without disputing anything the others have posted, i have personally put a 427 in a 69 convertible that started life with a 350. Nothing on the heater had to be changed.. full disclosure i used the SB frame brackets and motor mount cushions, but it fit fine.

 

Interesting,was it an AC car maybe? No way I could have hooked the hoses up on my '69 and I did the same just changed the mounts on the motor only.

 

Don't think it was an AC car. Had all non-AC stuff, including inside heat/defrost stuff.

 

Well I did have M/T valve covers,it had a big solid lifter cam that required taller valve covers and special rocker arms.

 

Found this, a 67 with a BB. Note the location of the heater hoses.

And heres a SB 67. Hoses where youd expect em.
You guys stumped me on this one. I'm quite sure the 350 car i converted had a heater like in the lower pic. That said, there sure seems to be a whole different set up for BB cars. Which is news to me. This is after owning one or another BBC car for almost 50 years. I've never seen a GM heater like the one in the top pic. They've all looked like the lower.

My 66 C2 is a BB and it also has a heater like in the lower pic. The hoses are easy access, valve cover installed.