Engine test stand.
 

I have just fully rebuilt the engine of my 2.5...every thing was replaced with new except the pistons, crank, main casings & heads...the crank casing was replaced with a good second hand 1 from a 3.2... it was damage due to the failure of the IMS...on start up cold it runs like a sewing machine...when hot & rev,s to 2,500 I get a very bad rattle coming from around the oil filter housing on the over run...it sounds like chain whip...after I strip & rebuild the motor...I want to build a test stand so I can run the engine before putting it back in the car...any idea,s.

Honestly, by the time you design a stand, get the material, cut, weld/bolt it all together you will spend more time then just mounting it in the car. I get what you are doing but time=money right?

No sure what "on the over run" means though.

Are you going to tear it down again and rebuild it a 2nd time?

engine test stand.
 

STL. :On the over run: means lifting of the throttle pedal & letting the engine coast... I can,t see I have any other choice BUT to strip the engine to find the cause of the noise...eventually something is going to cause a lot of damage.

No stand necessary, just sit it down on the oil pan, hook up some fuel lines and plug in harness

engine test stand.
 

When you say plug in the harness... you mean put the engine in the engine bay but not fitted to the car.

Thats probably your easiest way considering all the immobilizer issues.