ordered a vin air kit yesterday and one of the questions asked was whether my water pump had a short or long neck.
I thought all firebirds (68 with a 350 and turbo400) had same size neck and that maybe the GTO had the longer neck due to it having longer body/engine bay..
anyone out there know much bout this??

Here is a good explination of the water pumps and maybe this will help you figure out what you have. I would assume you have a short one based on the engine being a 68, but I dont know for sure since someone could have swapped something out over the years. Read the info and try to see what matches what you have on the engine now.
This is some really good info for 1st Gen owner's to save regarding water pump's being that there are two version's short and long.

All of the timing chain covers from 1964 to 1979 will bolt up and interchange with any motor from those years. However, you must use the matching water pump, pulley and crank pulley to avoid alignment problems with the alternator and/or power steering pump. All of the water pumps from ‘64-‘68 will interchange.

These pumps have eight bolts and measure 3-5/8” long (from base to water pump pulley flange). The casting number for ‘64-‘65 is 9772716 and for ‘66-‘68 it is 4782482. The matching pulleys are 2” in height. From ‘64-‘67 Pontiac used a small diameter (5.25”) six bolt two-piece harmonic damper and from 68-79 a large diameter (6.75”), one piece four bolt damper was used.

In ’69 Pontiac changed to an 11-bolt water pump but the early ’69 was different from late ’69-on.
Many early ’69 Firebirds and GTO's used a pump that measured 4” long (casting# 9796351) and the pulley was 2-1/4” in height. From late ’69 to ’79 only one pump style was used, it measured 4-1/2” long and there are at least two different casting numbers used: 482138 and 488296. The matching pulley should measure 2-5/8” in height. Always use the correct diameter and style crank pulley to match the water pump pulley and also use the same series timing chain cover and balancer to properly line up your timing marks. The same timing chain cover was used for both ‘64 & ‘65 and had just a simple pointer. These were cast with number 9773371.
The timing cover used on ’66 and ’67 employed a small timing scale marked -4, 0, and +6 and is otherwise identified as casting # 9783130. The ’68, ’69 and ’70 timing covers look very similar with timing marks of 0-6-12 degrees BTDC and accommodated the large diameter damper.
The ’68 timing cover casting number is 9790347 and uses the 8-bolt water pump. The ’69-‘70 timing cover casting number is 9796346 and uses the improved 11-bolt pump.
For ’71 and later the timing cover timing tab is marked from 4 degrees after to 12 degrees BTDC and is graduated all the way to 16 degrees BTDC. As compression ratios were lowered to 8:1 and lower there became a need for increased initial advance.
Casting number for this cover is 482883. If you need to order a water pump the Federal Mogul part numbers are: ‘64-’68 is FP1388N, early ’69 is FP1409N and late ’69-on is FP1423

Yes, ran into the long vs short water pumps on my 69 goat trying to get the right pulley. Spent $80 on the wrong pulley. That's quite a thorough water pump discussion there, Marine.

Thanks Bob, I also ran across the same problem, but was lucky to have run across that same discussion, saving me a lot of trouble.

Excellent info...but here's my question.

I just swapped out a 1968 400 for a 1969 428. The 428 has the 4.5" water pump and my pulleys don't line up with my accessories. I simply cannot line up my alternator at all. The crank pulley looks OK but the 68 water pump pulley on the 69 motor doesn't work. Any help??

You could probably use the 68 timing cover/water pump assembly on the 428 or else use all 69 pulleys (making sure you have the right 69 water pump pulley). I'm pretty sure all the assessory brackets (except AC?) are the same from 67 -69. My 69 goats have the same brackets as my 67 bird.

I think Bob is correct. You can use all the brackets, but would have to use all 69 pulleys to make it all line up together. I had a similair problem where someone put a non 69 WP pulley with nuts behind it to push it out towards the front on mine and I went looking for a correct pully and either I couldnt find one for a 69 with A/C or when I did find a stock one they were very expensive, I even tried repro and couldnt find one to match. Thats why I went with a complete set from CVF racing, turned out to look better (for me) and they all matched up. Off course if your looking for a stock look, which I think your past that since you went with a vintage A/C I wouldnt go that route.

thanks for the homework - will check out the info...and yes, engine is YJ block - which is a 2bl 350 with 2 speed auto which is what my bird originally was...