401 in a mid 70s crew cab

[GMJakers13]

Hello everyone! As the title reads, going to try and stuff the 401im picking up next week into a mid 70s crew cab c30. And im wondering if anybody on here has done the swap into those year model trucks, and what tips or ideas you all might have. The transmission I may get at a later date is a 5spd OD. But the truck is setup for automatic and dont know if there is a flexplate for the 401, or where I might find one. but I do have an NV 4500 on hand.... anything and everything is appreciated!

[bigblockv6]

If you're going to use an automatic then you will need the complete flywheel adapter housing flexplate from a Turbo 400 GMC pickup built from 66-69 provided you have the six bolt style flange crankshaft. Otherwise you can get a modern adapter setup from Bendtsens that just uses a flexplate and also requires a modern high speed reduction starter motor. Other things to consider are adapting earlier pickup V6 motor mount brackets to the frame and whether you are going to use an electric cooling fan or belt driven fan. If you use the belt driven fan then you will need the light duty pickup truck water pump housing which sits lower, that also requires using the 305,351 and 379 timing chain and sprockets which eliminates the 3 piece gear drive. I did a similar conversion on my 68 using the 478M but it was easier since the truck already was equipped with the 305E

[GMJakers13]

Nice. And thank you. I will be seeing it next week but does the 401 have a 6 bolt crank flange, being that it shares the same stroke as the smaller 305and 351, or is it the 8 bolt? Ive been told this engine is externally balanced. If so, I could probably make a flexplate. Just need to know what material would need to be used.

[bigblockv6]

Most are 6 bolt and later engines are 8 bolt, what year is the one you're getting?

[bigblockv6]

Originally Posted by bigblockv6

Most are 6 bolt and later engines are 8 bolt, what year is the one you're getting?

The 401 like the 305 and 351 are all internally balanced so there is no weight needed on the flywheel or flexplate

[GMJakers13]

Hallelujah! That makes things easier. Im not sure as to the year. Is there a reason they went from 6 to 8? Did things start coming apart? Again thanks. If its not external that means I can make am adapter kit no problem. The setup from Bendtsens is nice but a little pricey.

[bigblockv6]

The 478 always had the 8 bolt flywheel, it's possible things may have not been holding up with a 6 bolt in later years because 401's were in larger 7500-8500 series trucks. In your case a 1 ton Crew Cab will be fine with the 6 bolt setup. If you can make your own adapter that will be cost saving.

[Ed Snyder]

Originally Posted by GMJakers13

Hello everyone! As the title reads, going to try and stuff the 401im picking up next week into a mid 70s crew cab c30. And im wondering if anybody on here has done the swap into those year model trucks, and what tips or ideas you all might have. The transmission I may get at a later date is a 5spd OD. But the truck is setup for automatic and dont know if there is a flexplate for the 401, or where I might find one. but I do have an NV 4500 on hand.... anything and everything is appreciated!

Here are photos if the parts you'll need if you want to keep it stock, and not pay the big bucks for the Bendtsen parts. Note that the auto trans flywheel is different from the manual trans one. Send me a PM if you're interested in buying these parts.