I took your advice and finally mounted my Autometer mechanical fuel gauge on the hood (their 3 ft braided line is a good piece of kit)

I am using Carter street mechanical pump - and it gives me a constant 5lbs

I did a few passes last Saturday at the track - no lights - to see my fuel press during the run -

The first run was down to 2 lbs by just about the 1000ft and the last was 0 lbs. pressure!!!

This cant be good for my engine but you would not know it - the car went through strong -

I always thought the pump handled my car well - even when I switched from the Edelbrock 600 to my 650DP - since then I have been playing with jets and 74/73 jets & #31 shooters are my current setup

What do you think ? what should I do??

Sounds like a lot of jet for a 650. Your car will run on very little fuel pressure with few consequences, as long as the fuel level is adequate. We raced for over 200 miles in Mexico with the fuel pressure qauge bouncing off zero after experiencing a Mallory pump failure and installing a local electric 'bomba'.

among other things i would look for tight degree fittings in the fuel line, like 90 degree elbows. If you have tight fittings you want to replace them with sweeping style fittings (most performance fittings for AN lines have a sweeping style).
Look for any kinks in the line (look over the whole line, you may its crazy, but who knows maybe you put a slight kink in the line while installing it.
Restrictive fuel filters will with out a doubt have a bad effect on the fuel system, check out the filter to see if its rated for more flow then the pump.

What you DONT need is bigger fuel line.