Ticking Noise / Knocking Noise

My 2002 V6 Mustang doesn't tick until the engine warms
up fully. When I accelerate past 1,500 RPM it ticks and
gets faster as the RPM climbs, but only in 1st gear. When
it is in every other gear, it ticks really fast until about 2,700
- 3,000 RPM. In which case it stops. The ticks gets so fast
that it eventually turns into a rattling metal sound. After it
has been ticking for a bit, when I shift into Neutral the
RPM will stay at 1,100 and tick away. When I stop and
park, if I rev the engine, it's a knocking sound. Same goes
for Reverse. When the ticking has been going on for a
while, the car knocks in reverse. The car has a Rebuilt
Title and it sat in a driveway for over 4 months and hadn't
had an oil change in 12,000 miles, all the while it had a
small internal oil leak. I got the oil changed (it has a 3.8
liter and it only had 2.3 liters) and the sound just got
worse. I do not have the know how, the money, the
resources, or the money to figure out exactly what the
problem is. The car had aftermarket cat back dual exhaust
and had an aftermarket Intake / Intake Head. I'm
suspecting bad valve lifters or damaged pistons. I can't
afford another car. My previous car was a 1990 Toyota
Celica that broke down due to a blown engine, It had
268,000 miles. My 2002 V6 Mustang has 139,000.