Assuming you are talking about a Chevy 6-cylinder it would most likely be a short deck 194,230,250 or a tall deck 292 . . . you can tell it is a 292 if the side covers over the lifters / pushrods are about 6 inches tall. The short deck motors have side covers about 3-4 inches tall.

Casting numbers will tell you for sure.

It has the same bellhousing attachment as a small block chevy . . . the 292 has staggered motor mounts. Not a drop in / bolt in, but not a very difficult swap either. The easiest way to install will require a completely new drivetrain from fan to rear axle.