The "adjustment" at the rear is the fine tune of the pump timing. This pump is like a fuel pump and distributor all in one. all other adjustments are set at the factory or on specialized bench equipment costing tens of thousand of dollars.

I had my pump rebuilt and recalibrated and it cost over $800.

Again, this is nothing you monkey around with. You can do the timing adjustment, but you need a special dial indicator that fits that rear orfice after screw is completely removed. Then you turn the entire pump like a distributor and take measurements with the crank timing marks. The routine is in the manual and does require experience and specialized test equipment.

To do all this, you have to pull the radiator, accessory belts and fan and get them out of the way. You then have to pull crank pulleys and the timing belt covers. This is a good time to change the timing belts.

BUT... What adjustments did they make? Take it back to them and let them show you what they changed. or better yet, put it back. It's obvious it doesn't run, so they did something improperly.