[bigblockv6]

The lifters and push rods are the same. Timing covers definitely differ from light duty applications to medium and heavy duty applications. If you want to use the 305E timing cover then you will have to eliminate the timing gears and idler shaft on the 401 and cap off the hole where the idler shaft mounted with a 1 1/8 expansion plug and replace it with the 305 doubler roller timing sprocket and chain set. A good idea would be to fabricate a block off plate over the plug for some extra insurance, I did this on my 478M. If your truck is a 67-69 you can used the taller 401 housing but you will not be able to use the stock fan rather an electric fan. On 60-66 trucks you can remount the radiator in a higher position and retain a belt driven fan, anyway these arethe choices with such a conversion. The disadvantage of using 305 heads is they have smaller intake and exhaust valves as well as smaller ports over the 66 and up Magnum heads and the 401 won't run to it's potential. I 've seen some heads on ebay though a bit pricey.