is there any interchangeability with buick v8 parts like if i went out to buy a cam and lifter kit from summit and any clear way for all interchangeability as far as stroking it , it has an auto tranny and idk if it would hold up to a few more horsies

Yes and no.  The 4.0 doesn't have a distributor, so there are some camshaft differences.  Most people use the Buick 300 crankshaft to stroke them, it has a 3.4" stroke.  If you want to keep the crank driven oil pump you can offset grind the 4.6 crank to 3.4".

The cam also needs to be machined for the cam retaining plate of the later engines.

You can also stretch the 4.0 engine to 4.6 by using a 4.6 crank and rods and possibly retain the 4.0 pistons smaller 13cc bowls) for a hike in compression.

kevin.

I think you're right about the pistons, the 4.0 rod length is 6.1", where the 4.6 is 5.9"...so that should work out to the same compression height.

I was told that the 4.6 pistons were offset on the rods compared to the 4.0, is that correct?

Jeremy,

Both the 4.0 and 4.6 have a small offset so no problem to a straight swap of parts to achieve 4.6 which is actually 4552cc.

If and when you have the engine apart do check carefully for signs of  liner movement as the 4.0 blocks are the most prone to this problem, the 4.6 engines were built up from blocks with less casting core movement, just check all liners are sitting at the same height..

You should be able to find a scrapped 4.6 1/2 engine that has had a cracked block and use the crank & rods from that, if you use the 4.0 pistons it will raise the comp ratio to approx 11/1 which may be too high for road use or pump gas.

Kevin.