I currently have a 400 in my 69 firebird- i recently lucked on a 455 for cheap- i love the torque, but the horsepower is another story- would it be a wise idea to destroke a 455 and add some high flowing cylinder heads- to aid in higher rpms and possible horsepower- or is it just a bad idea all together-?  

There is a tremendous amount of power that can be coax out the 455 but what can be done and what you do  depends on two things, what you have and how much money do want to spend. To start how about some information like engine codes, you’ll find them on the block stamped on the front passenger sides of the block next to the timing chain cover and the head code found on top of the center two exhaust ports.  

the engine code is zj and the head code is 4x- 1973-455  

Man, check out wallaceracing.com they have charts with all the head and block codes on them. Scroll down the left side of the page until you see "head codes" and "pontiac engine codes" and check out the listings, I did and the only zj codes I found are for a 74 and 76 400, there is lots of useful info there on how to id your block and heads. Find out for sure what you have, then we can help you pick a combo.
Steve  

zz is the engine code sorry-and the head code is 4x  

Ok, the ZZ code 455 is a 215-250hp motor in 1973, with 114cc 4X heads it had about 8:1 compression with 2.11" intake and 1.66" exhaust valves. So what you have is no stormer to begin with, but it can be made better or way better depending on your budget. If you want to mildly build it, find some 5C or 6X heads off a 75-77 400, they have the same size valves and screw-in studs (all d-port heads flow similar #'s in stock form, given equal valve sizes)and with their smaller 101cc chambers will boost your compression to around 9:1, add a cam that matches your gearing/tire combo and an Edelbrock performer rpm with a good 750-800 cfm carb, headers and 2.5 or 3" duals. This will wake up the sleeping giant, or go the whole hog with aluminum heads, roller cam bigger intake and carb, the sky's the limit!
Steve  

In Oct 2006, I replaced the 326 in my clone '64 GTO convertible with a '71-'73 YC block overbored 0.06". Stock replacement pistons (+0.06"). I used 6X(4) heads with the exhaust valves opened to 1.77". I selected a stock-replacement HO Crane cam (Crane PN: 968781) for the Pontiac HO '068 and matching Crane hydraulic lifters. I use 1.6:1 roller-tipped rockers, an older Edelbrock Performer intake manifold, and Ram Air Restoration cast iron headers (3" header trimmed into a 2.5" dual exhuast, currently no crossover). I currently 'choke' the engine with an Edelbrock 600cfm carb, with eventual plans of upgrading to an Edelbrock 750cfm carb residing on my garage shelves.  I run a 700R4 transmission and a limited slip 3.55:1 rear end and P235/60R-15 BF Goodrich Radial T/As.  With a dry 3600lb curb weight, the streetable low-end acceleration of my car is fantastic - exactly what I was looking for!  I don't race, so this is a perfect combination for what I sought.

Good Luck Wishes with your plans!  

i like your set up, but how are you running a 700r tranny, i didnt think that they came with the bop bell housing design-?  

The 700r4 requires a bell housing adapter plate to bolt-up to BOP pattern engines.
Steve  

could  a  person order the adapter and so from summit, jegs, or?  

Yes they can be ordered from jegs for around $58.  

what all other mods had to be done to use the 700r4-diff shift linkage, modify the crossmember-etc?