ok...i asked earlier how to figure out the ratio of the rear-end in my 68 firebird....i did the "turn both rear tires one full revolution forward and count the turns of the driveshaft"......this came up the be about 2 3/4 turns....so i'm thinking its a 2.78...10-bolt....right???   ok my question is....is this enough rear-end for a 400 thats been modified with a torker intake and 650 cfm edelbrock carb and a turbo 400 tranny with a shift kit ?  just curious about your opinions....i just bought the car lately so i have no idea about whats inside the engine.  where do i look for #s on the heads ?? i found some #s on the heads casting, but dont know what they mean....if anything ?????

             A114....right side
             A074....left side  

never mind the question about where to find #s on the heads.......i found the answer at year one  

I would recomend using a 3.42 gear ratio for the street and a 3.73-4.10 for race use this also depends on the size tires being used.  

First the head #'s you listed are the production dates- January 7th and Jan 11th of either 64 or 74- likely 74. What are the numbers cast into the top of the centre exhaust ports? They will tell more about the heads.
As for your gears, you are right, probably in the 2.73- 2.78 range, whatever was available back then. Pontiacman8 is right about the gear ratios he listed, they will make a world of difference in performance. But it really depends on how you will be driving it, if you intend to drive it cross-country, stick with the highway gears. If it never leaves the city limits, gear the wee out of it and have fun!  

ok...more info... the only other numbers (letters) i could find are D   N....... and a big 4X on the head..........i learned at year-one that the 4X was for a 265hp 400....and the DN means it has D-port heads.   please correct me if i'm wrong

and again, thanx for all ya'lls help !!


ps...where do i find a 3.73 or 4.11 rear-end...what interchanges  

Your info is mostly correct, except the D and N, if you look closely at your heads you will see an arrow between the D and N pointing at D for Dayshift or N for Nightshift. 4X heads came in both large and small valves and with or without screw-in studs depending on build date. I'll check my books and see what yours should be.
Richmond gear makes gears for your axle, check Summit racing.  

The 400 with 4x heads was rated at 200 to 230h.p. with a 4 barrel carb. they  have 98cc combustion chambers and 2.11/1.66 valves. there is also one other code  needed to identify the heads as 400 or 455 heads as they were used on both on the exhaust port side of the heads in small print you should find a code 1h,3h,4h,or 7h.  

ok thanx.....i'll look closer and reply  

no luck....maybe im not lookin in the right places , but the only other info i can find is a  G M 8 on the exhaust side  

Ok there are 2 rectangular shapes by the exhuast ports one will have a threaded bolt hole and the other will have the code on it and it is alot smaller print then the other codes.