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Old January 30th, 2019, 01:58 AM
azcbass azcbass is offline
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Join Date: Jan 2013
Location: Tucson AZ
Truck: 1966 305 C with a Camper Convertion
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Default Swapping out a 305 for 351 or 401?

Well i was ready to pull the trigger on that 351 a lot of you helped me rule out was not a magnum.. But when i got back over there to do a compression test i found that the oil cover under the air intake manifold had a lot of dirt on it. As i was cleaning out the space around the plugs, I just barely touched the cover with a scrapper and it caved in, rusted out. But we continued on and tested the number 6 cylinder, it came back at 90 psi after about 8-9 cranks. I had to pump the breaks right there! So still on the hunt for a 351 or 401. Heeeewww dodged a bullet there....

I have some questions....

Let me just preface this here that im no SAE mechanic! Im not a complete idiot but in no way have i ever tried to do what im attempting with this motor swap. Luckily i have some guys that i trust that are and have all the resources needed to pull it off. Im trying to get some more info on what i might be in for.

So I got a few questions on going from a 305 to a 351-401

1. What important parts are NOT interchangeable?

2. Are these the exact same blocks with just different bores?

3. Where should i be looking for signs of needing a rebuild or major tear down?

4. If i need all new seals whats my best resource to find them, can i find them?

5. Can i get rings, bearings, pistons all that is needed to do a rebuild? If so where..

6. What don't i know that i should be asking?

7. Ill stop there for now.

Thanks for any n all feedback.

66 GMC Open Road Camper
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Old January 30th, 2019, 06:24 AM
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63gmc4x4 63gmc4x4 is offline
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Location: Orem,utah
Truck: 62 custom 1000, 63 K1000
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Default Re: Swapping out a 305 for 351 or 401?

305 and 351 are the same block I just swapped mine from 305, problem is there is no head gaskets for the 351 or rings or pistons,and if it's the magnum or 351E you will have make your own intake and exhaust gaskets and have a carb adapter made to fit the trapizod base , parts will have to be custom made or get lucky on Ebay, I would start with a know great running engine and cleanup and drop in!
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Old January 31st, 2019, 01:10 AM
James James is offline
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Join Date: Jun 2013
Location: Greer, SC
Truck: 1964 GMC 1500 2wd
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Default Re: Swapping out a 305 for 351 or 401?

Check on ebay for 351 head gaskets. To me it is a bit pricey.


Last edited by James; January 31st, 2019 at 01:10 AM. Reason: added info.
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