".. I can handle flaming.."
I'm sorry, but I'm an old country boy. I don't have a clue what "flaming" is. Oh well.
Anyhow, all 455 engines came with Q-jet carbs. Most were 750cfm. A few were 800cfm.
The 650 is too small for a 455. IMO.
"...Can I source a rebuildabke core from a junk yard..."
Maybe. Depends on the yard. The best Q-jets came on '76-'79 cars. Some of the '68-'74 carbs are good too. Also, Edelbrock made some good Q-jets. These are actually newer than the GM Q's.
Besides cfm rating, there are other differences in Q-jets. Most BOP Q's have a straight front fuel inlet. Most Chevy and all Edel Q's have a 90 degree, sometimes called a side inlet. You can use either kind, on a Pontiac engine. But, there will be some additional plumbing, for a side inlet Q.
Most every car maker used a different throttle lever/cable hook up. So, depending on the exact model Q you get, you may have to fab your own throttle linkage. Also, some Olds and Buick Q's had a throttle return spring that pulled from the front, instead of the rear.
All Pontiac Q's beginning in late 1970 thru '79 had a big "smokestack" bowl vent, which requires a hole for it, in the air cleaner base. Also need to use a rubber grommet to help seal the hole around the vent, to prevent any trash or dust from being sucked into the carb.
The '76-'79 Q's have a desirable adjustment feature, which is referred to as an APT.
If you don't want to have to deal with the big vent, but would like to have the APT feature, you can source a Q for an Olds 403 engine. There are others, but these came on lots of 403 TA's, in the late '70's.
If you'd rather just buy a good Q, there are some good builders around. These 1st two I'll link are both known as good Q-jet sources.
http://www.everyday-performance.com/quadrajet_carburetors.htm
http://www.smicarburetor.com/products/sfID1/28/sfID2/9/sfID3/100
There are lots of Q's for sale on Ebay. Some are good, but some are probably not so good.
http://www.ebay.com/itm/Edelbrock-Quadrajet-1903-Remanufactured-Carburetor-795-CFM-/171961410486?hash=item2809b2e3b6:g:75QAAOSwYHxWMVZo&vxp=mtr
Summit sells UREMCO rebuilds which may be OK. I think a member here bought one of these not too long ago. But, right now, I can't remember who it was. Maybe he'll see this post and tell us how his UREMCO is doing. :smile22:
http://www.uremcoinc.com/carburetors/view/35919
http://www.summitracing.com/parts/urm-11-1230
http://www.uremcoinc.com/carburetors/view/37711
http://www.summitracing.com/parts/urm-14-4200