You should use the computer, or at least the chip from a car with a 350 in it.
There could be a number of issues. Did he use the whole engine, or just the long block? Are the wires that go under the front of the engine serviceable?
What condition is your cat in (if it is clogged, it will run poorly). My car would not go over 45 when the cat was partially clogged.
Check your fuel pressure if you can. You must have 9 PSI minimum. You may need a fuel pressure regulator, if he used the TBI that came with the engine.
I believe that the spark control module (on the relay bracket) is engine size specific (350 with 350), but the engine will run with the unit used with the 305.
Make sure all of the wires are in good condition. If the insulation is cracked/missing, it will affect the running of the engine.
Replacing the bearings will not cure a rod knock. It may silence it for a short time, but it will be back with a vengeance. Usually the rod journal is damaged when a bearing is worn. A knock can be the rod bearing or the wrist pin. If it is just a tick, it can be a lifter. An engine stethoscope can help you find the specific location of the noise.
A swap of the engine and trans is a 2 day job at the most. If a long block is used (your old intake installed), it may take an extra day.
If the timing sets with the connector disconnected, it is not your distributor or timing chain. Timing is "0" with the connector disconnected. If the connector is not disconnected when setting the timing, the timing will be wrong, and the engine will not run properly.
I paid someone $350 "install" a used engine for me. I picked the engine, and got it to him. I still ended up finishing the job myself. I also had to replace the oil pump after the engine was installed. It took 2 months to get the job done with all of the BS, and excuses. If you have an engine and trans to install, you can do it in two days...pull the wiring harness with the engine, and install the harness on the donor engine before installing the engine and trans. If I were getting paid as much as you paid your guy for installing a used engine, I would probably be able to get it done in one day, especially if I had power tools, and a complete shop to work in.
My engine in the 92 came from an RMS with 135K on the clock. It now has about 155K on it. It does not smoke, or leak, and performs like it should. I am going to re-ring the 350 that I installed in my 91, and put it in the 92. I will offer the engine in my 92 for sale after the swap. Complete from TBI to pan, including the exhaust manifolds. I will also sell the trans, but I think it needs a torque converter.
If you can get an engine from a truck, it will have 4 bolt mains, but you need to use your original manifold and distributor (you can get a new distributor on ebay for about $73). A 93 9C1 engine will have a hotter cam, bigger injectors, and you need the computer from the same car.
1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, custom fender skirts, Impala rims, Recaros, Blazer console, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
1992 OCC now with 5.7 tbi, DEH P77DH
For a parts list, check http://www.impalassforum.com/vBullet...1#post11691762