1992 toyota pickup

Here is the situation... i had 3 burnt out valves in my engine, the
22re, and i let some moron rebuild it. i got it back and there was a
knocking noise in the engine.. he claims it was the valves.. so i was
like whatever, my truck runs, i can go from point a to point b. its all
good. the noise got worse so i took it to my friends private mechanic.
i told him it was the valves and that he didnt need to listen to it,
so he went ahead and tuned the valves. many of the valves were too
tight. not good right? well. after tuning them, we put the cover back
on.. and the noise is still there.... its pretty damn bad. i take it
to my friends house and he has a look at, listens with a stethoscope
and we found out its coming from the front left of the engine, if ur
facing the truck... so we thought, mabye the mechanic didnt tune it
right... so we go ahead and take the valve cover off again... check
ALL the valves, and guess what, they are all perfect. the noise is
still there, so he thinks, mabye its a piston noise. we unplug one
spark plug at a time, 1, 2, and then we get to 3... we unplug 3, and
the engine idle doesnt even drop! my third piston, is pretty much
DEAD! that doesnt make me too happy.... we pay a guy 2 grand to fix my
engine and the third piston dont even work... that just pisses me
off... i want to get a new truck, but cant afford it. so im
wondering... can i drop a v6 in there on the same transmission? or
would i need a v6 transmission....? also, i have heard that the v6 is
kinda gutless so... should i get the v6 tranny and get the lexus 1uz
v8? or the 3.4 L v6 from a newer taco? plz advize... ill do anything
if i can keep my 4 wheel drive....