I was wondering if there are any differences in between the 12a blocks for the 79-85yrs?
As far as the blocks are concerned anyhow.

Can I drop an 85 into an 81?

 

yes yes yes, I did a write on our local forum not long ago yes 85 into 81 as far as I know, the 79 & 80 are different as they are the thermal reactor engines

Am at work otherwise I'd get more in debt

 

I think you mean depth. Unless you get charged per word on this forum and you ran out of typing money.

 

there's no real differences as far as them mounting in the car and gotten to run.

 

the only difference is the rotating mass. make sure you use a flywheel from an 85 on an 85 motor. 81-82 motors are the same and 83-85 motors are the same. The expernal parts of both motors are the same.

 

Beehive vs short filter pedestal. Also T-shaped steel heater core fitting on rear plate vs short straight fitting. Your stock rubber heater hose will work on either style of fitting. I've had an '83-'85 engine in my '81; hose worked fine on rear facing nipple.