I recently discovered that the heads on my '70 Cutlass 350 are #8, which evidently are smog heads from mid-70's. Therefore, looking for #5-7 to replace. Any advice on where to find, price, and what to look for in evaluating condition?

 

Welcome to the site!
Place a thread on the "Parts Wanted" section. Also post your location, city/state. I know there are several of us on here that have extra heads of those castings (example see my ad under "parts for sale") But why pay to ship a set all the way across the country if someone in the next state has a pair? I like to have them hot tanked and magnifluxed before shipping. You can do a visual for cracks, but having them cleaned and magged is a little better bet to verify there's no cracks. My 2 cents worth! John

 

i have 6 and 7 heads in indiana.

 

Smog heads?
These heads are virtually identical to #7 heads, only that the #8 heads have an 80cc chamber. The #7 heads have a 68cc chamber, making it breeze for you to raise compression. If you are going to be daily driving this thing, you would be well off to keep the #8's.
Ports are identical
Valves are identical
Both have hard seats
The only thing the earlier heads will do is raise compression (power increase will be from that alone), but you will have to use a premium fuel.

What are the plans for this engine/Car?

Jim

 

Well, my plan is to get it to driver condition but trying to keep as original as possible.

 

Well, the next question is...is the block original?
If the block is original, I can see the #7's.
If not, I do not think originality is much of an issue, plus the pistons they used with #8 heads may cause detonation from hell, with a short camshaft, and #7's.
WHAT YEAR was the block manufactured?
Was it ever rebuilt?
What pistons does it have, what dish (cc's)?
I can see someone bolting on #8's to lower compression, and aid drivabilty, I can also see someone swapping out to a later engine completely.
Driveability is the main concern, and I would find out what exactly I had between the frame rails before any purchases were made.
JMO
Jim

 

Sounds like its more complicated than I thought-I figured the older heads would raise compression and result in a bit more power. It feels a bit anemic now, but overall the motor sounds solid. The block is 68-70, but I don't think its orginal to the car (still can't find the serial # on the block). I don't know if it was ever rebuilt-I've only owned in 6 months. So you think putting the older heads on without digging deeper is a risk?

 

No, you just want to know exactly what is going on.
First off, find the serial #.
From the wiki site:

1968-later V-8 Engine Have the last six digits of the VIN number, the year of the block, and the assembly plant stamped on the driver's side of the block below the cylinder head. A 2-letter code on the oil filler tube identified the engine.
You can use the VIN derivative number to ID the year. For 1968 and up blocks, this number is located on a pad just below the cylinder head on the front left side of the engine. This number will be stamped on a machined pad on the front driver's side of the block, just below the deck surface. Typically it will be covered with a power steering bracket or something, below the number one spark plug location.
This number should take the form of "35Mxxxxxx" where:
3 = Oldsmobile division.
5 = year of manufacture (8=68, 9=69, 0=70, ..., 4=74, 5=75, 6=76, etc.).
M = location of manufacture (M = Lansing, B=Baltimore, X = Kansas City, Z = Fremont, CA, etc).
xxxxxx = last six digits of VIN of car that motor originally came in (original car's sequential production number).

Find out what you have.
Jim