I have a 1984 elky with a 305 what tranny is most likely in it?

If it is a three speed, it is a THD 200. If it is an overdrive, it is a 200 4R. Neither of these are very strong units. I've had 4 ElCaminos and the 200 / 2004Rs are not that reliable. My current 86 SS has the 200 4R and has been OK, but the torque converter clutch (lockup torque converter) is sticking with only 66,000 miles on it. My previous 85 El Camino wth the THD 200 three speed failed at about 50,000 miles. I also had a 79 Malibu wagon with the THD 200 and it was replaced 4 times in 16,000 miles. Anyway you didin't ask about my experiences, but for what it is worth, this series transmission was not one of the Generals better efforts....

Is there any possibilty it is a th350?

I'm wondering the same thing

because the mechanic I took it to said it was a TH350...and I'm wondering if they came with those ('84, 305, 3 speed I think)

Turbo 350 lockup to quote him

I've had several El Caminos and only one had a 350. It was a 78 SS (factorySS, not Choo Choo Customs). I had an 81 that had a THD 250 which looks similar to a 350 but not as strong. It may be that someone installed a 350 if you aren't the original owner??

Here's a very helpful document for identifying which type of transmission you may have: Transmission Identification (http://www.nastyz28.com/transid.html)

it is a TH350

meso happy :-D