Big block swap

[jonnymel]

1960 GMC
Ok , i took out my tired 305 out and put in a fresh 454 . The first problem im having is my valve covers are tight against the firewall. So tight i wouldnt be able to remove them.
My valve covers are after market cast aluminum holleys. Would a stock pair of 454 covers be smaller and gain me some clearance or is there a different motor mount with an offset that i should be using??
Im pretty inexperienced at all this stuff but really enjoy trying to do it on my own or with advice from people who know how.

[Old Truck Man]

I installed a 427 with stock valve covers in a 63 pk. I took a BFH and massaged the firewall until I had enough clearance.

[Captainfab]

Even stock valve covers won't give you enough clearance with a big block on the original engine mount brackets. There are a few different mounts to use. One would be the '68-'71 big block engine mount brackets. Next would be the '67-'72 small block engine mount brackets. Or the '73-'87 complete engine mounts and brackets from a C20 or 30. Then there are the aftermarket tubular mounts. But if you move the engine forward, you will also have to move the trans forward. There are quite a few forum members with big blocks in their trucks. Some of them have just notched the firewall to accomodate. When I put the 454 in my Suburban, I fabricated my own mounts and moved the engine forward 2" or so using the '73+ clamshell mounts.

[64-454ss]

I have stock valve covers on my 454 with engine in the same location my 350 was in. Very tight, but they clear with just enough clearance that I can pull em off. Had issues with my existing headers and even stock cast manifolds hitting stock mounts, so I used a motor plate and removed stock mounts once plate was finished. A little more research and a few more bucks and I could have just bought headers that fit correct but money was an issue at time after I blew up the 350. Been told mid 70's big block headers for a Chevelle will fit nice.

[jonnymel]

Thanks guys
I took a piece of 1 1/4 round pipe and a hammer and used the pipe to make a nice smooth indent in the firewall. It's not perfect but looks pretty good, a little paint and I'll be happy.
Next step put the motor and tranny back in.
I'm still not sure what headers or manifolds to use. It sure would be nice have some on hand to try before I buy.

[BigSix]

Awesome project! I am thinking of pulling my 305 for a big block but my only reservation is that my 305 is the best running engine I have owned! It just doesn't have 400hp

[jonnymel]

The 305 would obviously be more practical . I've never even driven a big block so I'm pretty excited. I got a sweet deal on a fresh rebuild , my buddy is a mechanic and he gave me a motor and his shop rebuilt it. It should be 500hp plus.
Nice to have good friends

[Captainfab]

On my Suburban I used '73+ pickup headers, but they do hang down more than most guys like. You will have to trim the top flange of the frame a little for any header, or manifold to fit correctly. Are you keeping the manual trans or are you converting to an auto trans?

[jonnymel]

I have an existing th400. I will be re-using it.
Thanks for the info regarding the exhaust.

[Captainfab]

An auto trans is easier to move forward to get the needed valve cover to firewall clearance. You'll need a longer driveshaft though.

Originally Posted by jonnymel

I have an existing th400. I will be re-using it.
Thanks for the info regarding the exhaust.