Flyweel help

[Farm boy]

ok so i am swapping my 86 k10 from a th350 to a sm465 (for more info: http://forum.73-87chevytrucks.com/smforum/index.php/topic,24069.0.html ). so i got the th350 out and got the flex plate off but when i went to put on the new flywheel i found out that the center whole and bolt pattern are to small on the new flywheel. so i compared it to the engine i pulled from my 80 k10 (both engines are 350s) and it will fit on that one. so my question is what do i need to know in order to by the right flywheel this time (these puppies cost too much to keep trying a different one;). oh 2 more things 1 the engine is not the original engine 2 i think it has a external ballenser (i don't really know what that looks like but the "hub" of sorts on the back of the crank isn't round).

i don't know exactly what info you need (or if i used the wrong term making it unclear) so if you need something ask worst case is i ether look or just don't know

[Blazin]

Not sure what engine your talking about when you say 2 more things? The one you pulled the flywheel off of, or the one your trying to put it on in the 86?
Sounds to me like your are trying to install a one piece rear main seal flywheel on a two piece rear main seal motor, or visa versa.
Which side is the dipstick on the motor in your 86?
If its the LH side its a two piece rear main motor.
If its the RH side its a one piece rear main motor.
You will need a flywheel, and bolts to match the correct rear main seal.
Loctite the bolts too!
You will also need to know the clutch diameter of the new clutch you are using when buying the flywheel.
Double check the tooth count of the flex plate as well to be sure it is the same on the new ring gear to match the starter.

[Farm boy]

Well although i had you confused (going back over it i wasn't real clear on that), you told me what i need to know: the size of "hub" on the back of the crank if ether big-2 piece seal, or smaller-1 piece seal. so i will be ordering a new flywheel now. btw to try and clear it up for you i am working on a 86 and i'm not swapping the engine right now, what i was referring to was i plan to rebuild the engine from the 80 that is now sitting in the shop bc im parting out the truck it came out of. the flywheel is new from rock auto, both my trucks were autos but now im converting the 86. Did that help clear it up at all?