I was looking at a local ad that reads as follows:
I have a set of the super desirable 1972 Oldsmobile 7A 64cc chamber heads. These heads are generally swapped on to olds 403 a for compression increase and these particular set of heads have already been updated with a larger valves set from Mondello Performance. The head have been built by a machine shop, surfaces and the head bolt holes drilled out to 1/2in to accommodate the larger head bolts of the olds 403. If your looking to ad some performance to you olds 403 trans am or firebird, or any other olds 403 equipped vehicle, these heads will make a serious difference.

$600 OBO

k was wonder if you can just drill out the holes on the block for the head bolts for 1/2, can you put these back on and if it would be worth the $600.

 

Any time an ad says "super desirable", you can bet the price is too high. The first question is, exactly what size valve were installed? The second question is, what did the machine shop do, exactly?

 

If the bolt flanges are too small from the holes in the head being enlarged I don't see why you couldn't have the block drilled and tapped to match; but, Id look for studs, nuts and washers to remedy the situation. Other members will chime in, some have probably already done this.

Get the answers to what Joe asked, it matters.

Good luck!!!

 

The head bolt holes are no issue. The dowel pins are what locate the head on the block. The bolt holes are clearance holes anyway. Just bolt them together with normal 7/16" head bolts and good washers.

 

There are reducing sleeves available also. They are very common on Small Block Ford aluminum heads because the 351 uses a 1/2" bolt and the 302 is 7/16

 

Yes, they do, I used them on my #6 heads that were drilled for 1/2" bolts. They are bigger than 1/2" where they go into the head. A stepped drill bit will work best to fit them.

 

I have a pair of #4 bare casting- smallest as cast head. Have a set of my 403. Look stock.