Recently had a 440 built & installed in my ‘73 E body (originally sb car)… passenger side of motor keeps slipping down to the point it sits on the tie rod & is wearing through my tti header tube.. any ideas how/why it is happening?

Post pictures of your mounts.

What motor mounts did you use, no BB installed by the factory in those cars that year

all he needed was 66-72 bb backets

so it was fine. then changed. So something has moved, slipped, or broken. You first need to look in that area for "The Obvious".
Then report back here.

Wrong oil pan for that body and spool type motor mounts

E-Bodies never used spool type mounts.
As far as the oil pan, I guess it depends on exactly what kind or type of oil pan that he used.

Wasn't 1973 the first and only year that Mopar used the Spool type K members in E bodies?
Also didn't they not offer BB in E bodies in 1973?
If the motor he used to out in his car came out of a C body it will have lower, deeper oil pan behind the center oil pan sump than B bodies did

Probably worn or soft engine mount insulators. Hard to find good ones anymore. I have to use a torque strap on my Big block cars. Probably not a bad idea for your car.

No, they never changed the style of motor mounts on an E-Body. 74 was the last year for E-Bodies.
He should have been able to use the mount brackets and rubber mounts from any 66-72 big block Mopar engine as was already stated.

It's not the oil pan that's rubbing it's the TTI header

It's probably a bad/weak rubber engine mount/insulator that's the problem.

I ordered a sb to bb kit from schumacher & even splurged for the polylock mounts

Also have schumacher torque strap installed

Actually had motor/trans w/ a g.v. Od unit installed & rear done… got it back months later noticed motor was uneven.. loosen all mounts (trans too) & brackets, level motor retighten everything & w/in a week motor slides down again

I'm thinking the tightened bolts are not tightening enough. Maybe you need to add a flat washer under the lock washer and the nut on the bracket side of the motor mount. I would do the extra washer on both sides of both rubber mount/brackets. Maybe someone cut the slot in the bracket too long.

its also possible the headers are at the wrong end of the allowable tolerance and the tube is too close. Can you hammer clearance the header tubes for extra clearance?

With your description that it was correct and the motor sat level, then a week later the motor was no longer level and the header was rubbing, I would go with the extra flat washers 1st.

I agree with poorboy, add washer first. The only thing I would add is make sure you use grade 8 washers.

Are you lifting the engine so everything is topped out ?

If so this is your first problem , you need to loosen the bolts and let it all drop into place and the only real adjustment is leveling side to side , you can't have the bolts holding the engine UP to give you needed clearance because the vibration is just going to let it all slide back down. Sounds like you need to clearance the header tube?

Interesting... I recently encountered a similar out-of-flat-level with my SB... using the Schumacher poly-mounts. It appeared to be small... maybe only 2-3-4 degrees out-of-level. The steering linkage (idler arm) was slightly rubbing against the headers. Those mounts MAY have to be massaged to fit the dowel-pin into the factory k-frame... I did that... and you can compare the dowel pins... they are NOT the same (Schumacher vs OE rubber type). However, I still had to loosen ALL the bolts... motor mount bolts, exhaust/header bolts at the collector, trans mount, lower and upper radiator hoses... everywhere! Then, re-settle the engine back down into the k-frame.. flat as I could see ... and re-tighten ALL the bolts.

Actually, I think the Schumacher mounts aren't as TALL as the factory typical rubber mounts.... thus... lowering the engine slightly which welcomes interference with the headers and steering linkage... in particular.. my longer C-Body IDLER ARM (aka: Fast Ratio).. no problem with the factory FAST RATIO PITMAN ARM. Granted, most of us are not running this setup as I am, but... it was a surprise to me when using the Schumacher poly mounts.

BUT, I will say, the rubber mounts have a huge amount of twist and flex... incredible amount!!!... just put one into a vise and twist and see... unbelievable amount of twist!

The Schumacher mounts do NOT give any additional noticeable vibration... which is good.... nothing to be concerned about.

There's no problem installing a BB into a V8 E-body k-frame... just use the correct common motor mounts.

Hope this is helpful.

That's your problem right there, the durometer, as well as the poly used for their mounts softens/melts from engine/compartment heat causing the mount to collapse, headers exacerbates the condition.....

Thanks for all insight/advice… i am going to order a new set of original mounts & add the extra flat washers and/or lock washers… will see how it goes & will post results when done