1967-68 and 1969 a-body big block exhaust systems were two completely different configurations including the pipe sizes. 1967-68 were equipped with a two piece head pipe that were 2.25" O.D. at the front and midway back were downsized to 2" O.D. pipe to the mufflers. The mufflers were 2" I.D. in and out. The factory welds were where the 2" met the 2.25" head pipe (below the front seat area) and the mufflers were welded directly to the 2" head pipe sections. Not a pretty exhaust system to look at.
1969 (383/440) head pipes were 2.50" O.D. one piece units with the mufflers being welded directly to the head pipes. A cleaner appearance and better flow than 1967-68 head pipes.
Tailpipes were different as well between the years. Here is a description of the 1969 units which we also use for all years that were exhaust tip equipped.
http://www.accurateltd.com/One-Pair-of-Tailpipes-for-tips--225-or-250-A-Body_p_202.html
The only time we would supply a 2" tailpipe is if it was special ordered and this would be incorrect for 1969 except for the two piece factory units which would be 2.25" at the front (muffler end) and 2" at the rear-then sized down to 1-7/8 I.D. for the exhaust tips. The 1968 tailpipes were 2" at the front (muffler end) and 1-7/8" at the rear.Then these were sized to 1-7/8" I.D. for the chrome tips. The 1967 big block a-body models were not chrome tip equipped and were 2" at the front (muffler end) and then an 1-7/8" O.D. section was welded in (near the front of the fuel tank) back which included the turn down section at the rear. Changing the 1967-68 O.E.M. exhaust system to the later 1969 configuration with a full 2.25" exhaust system is an improvement in both appearance and flow. But increasing the size to 2.25" from the front to the back does increase the noise level over the smaller original exhaust system. Altering cam profile, induction and other parts also changes the exhaust note and most of the time increasing interior resonation under load and certain rpms. Just a few things to consider when deciding what exhaust system is right for your combination.
Tom