hey guys how much work would it be to put a 351 with a carb in a 91 t bird that as a 3.8 in it
will i need a new tranny gas tank will it fit ??

You may need
A computer system for the new motor with the wiring harness.
New exaust
Possible a compatible transmission.ect

yeah it will fit. but if its an automatic your going to need a new trans and if its a stick you may get luckey and just have to replace the bellhousing.your going to have to put in a new exhaust and the cooling system is going to need some work.