What kind of epoxy do I use to install a new pick up in my oil pan .I just bought some new Hardin Pans and the cut out in the windage tray is on the right side .Any suggestion ?

Braze it.

braze or mig it or press in using locktite sleeve retainer

I wouldnt epoxy it, wont hold for long. small tack weld is the best

can you tack weld while installed on the block

Yep.
Just hit it at a spot. not all the way around

Boatman,
The correct way to do it is to remove the pump from the engine, take the cover off the pump, remove the gears, install the screen and check it to see if it is the proper distance from the bottom of the pan ( about 1/2" ) ....... then have it TIG welded or brazed. Then clean it and put it all back together. Then reinstall it on the engine.