10 bolt to 12 bolt swap

[a66boo]

I recently acquired a 12 bolt 3.40 gov-loc posi rear from a 1979 1/2 ton shortbed that I want to bolt in my 1985 1/2 ton that has it's original open 10 bolt rear... This leads me to the u-joint dilemma where the original 10 bolt yolk was larger than the 12 bolt.  Does anyone know either the physical measurements for the proper u-joint size that bolts into the 12 bolt so I can try to fins a conversion joint to adapter?  Or better yet happen to know a part number for the conversion u-joint!?
Thanks for your time...

[Irish_Alley]

i don't know any joints numbers but what i did at autozone when i worked there bring both joints or get them to get them from behind the counter and then get them to find a similar joint with two ends that match the size and leanth of the 85 and the other two that match the 79

[VileZambonie]

Here's one I used http://forum.73-87chevytrucks.com/smforum/index.php?topic=7334.75

[a66boo]

Thanks Guys!!   I searched and searched, apparently I don't search well!
Vile, Thanks a million!!

[a66boo]

Just for clarification and assistance to possible future folks searching on this subject.....

The Corporate 10 bolt 8.5 inch rear on my 1985 1/2 ton 4x2 uses a 3R size joint on the drive shaft and yolk.

The 12 bolt from a 1979 1/2 ton 4x2 uses a 1310 size joint on the yolk.

A conversion u-joint would be available: Here's a source

http://www.dennysdriveshaft.com/p466_1310_to_gm_3r_s44_series_combination_u_joint...spicer_grease.html

Or

http://www.theujointstore.com/33131.html