I have an '84 Firebird, it has a bad pontiac 350 in it, I have a chevy 350, will the tranny bolt up?

 

are you sure it is a pontiac motor? ... i thought they all got chevy motors ... if it is a pontiac motor, the bell of the trans will not be the same ... the top of the chevy bell will go up, where as the top of the bell on a b.o.p. will go down

B.O.P. like this http://www.novak-adapt.com/images/pi...ellhousing.jpg

Chevy like this
http://pitstopusa.com/images/F14587414.jpg

 

They all go chevy motors but nothing from 84 got a 350 so it is probably a swap.

Take a picture and we can identify it.

 

It would be a little interesting to see what was done. Third gens did not come with anything other than a chev engine. If someone swapped in a 350 chev, then there isn't a big deal. If they stuffed a pontiac engine under the hood then there's normally more than just an engine swap involved.

The third gen Chev transmissions only came with the chev bellhousing bolt pattern however GM also made transmission cases with dual patterns. BOP and Chev so they could be attached to all the V8's including Caddy. An adapter plate may have been used to attach a chev pattern trans bellhousing to a BOP engine but if it has a pontiac engine it may also have a BOP only pattern transmission. Since third gens use torque arm suspension, there needs to be some way to attach the torque arm to the back of the transmission since only 3rd and 4th gen transmissions have a built in mount on the tailshaft housing for the torque arm. An aftermarket torque arm could be used to move the mount off the housing.

If a BOP pattern trans was used then it's probably not an OD tranny. More likely an TH350 or TH400.

No matter what, it's probably not original and as stated above, lots of pictures would help. If the transmission is original and the engine has been swapped for a pontiac engine with an adapter plate for the transmission then putting a 350 chev into is a basic swap back to an original chev V8 setup.