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Engine/transmission swap 720 L20B/5sp into 520?

Phil P

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Hey everyone I'm new and need advice. I have a L20B and 5 speed transmission Removed from 1980 King cab 4X4 720. Want to put it in my 1967 single head light 520. I understand that a L20B will fit? Looks like the oil pan is going to have to be changed? TY Phil

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The 520 is a very tight fit for an L series engine.


The frame engine mount locations are set up for the J13 which will not take an L series engine. You'll need to cut them off and move them.


You will need, for convenience, the oil pan from a 521 with an L16 engine. As the 520/521/620 and 720 are somewhat similar front ends with the steering in the front, and as you are completely changing the engine mount locations you may be able to use the 720 oil pan.


The 4x4 does not have a speedometer drive in the transmission nor can you fix this without swapping a 2wd tail and worm gear onto the main shaft onto it.


Measure the transmission length. The 720 had two different lengths. If you have the 26" 'shorty' you may not have to modify the driveshaft length.



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It appears the 720 oil pan on the 4X4 is different from 720 2wd.. The oil pan is offset and larger on the drivers side, in the rear. It is to clear the front differential and front drive shaft. The dipstick is in between the engine and the firewall into the back of the engine.

1) Will that dipstick work with the 521 oil pan? 

2) If I change oil pans, will I need to replace the pick for the oil pump?


TY Phil


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Oil pickups match oil pans they are a set so to say. 


As far as the dip stick and tube compare the 521 with the 720.


I installed a L20B automatic in my 66 520 and it is well documented in my 520 build thread orange link in my posts.

Edited by Charlie69
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Do a complete chassis swap.  I did a 1980 720 chassis swap to my 66 520.  Best upgrade I did.  It gets you away from King pins gives you disk brakes and removable trans cross member.  also gives you rag joint steering column and the idler arm and steering gear box is outside the frame rails.  This is also documented in my 520 build thread.


Wayno has done several 720 to 520/521 chassis swaps.  Wayno is a great source for information.

Edited by Charlie69
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