3406 is longer, i am not sure by how much though. another option is a 3306 which would be a little shorter. alot of d336's died an early death. one problem that htey had was overheating easily and cracking the heads.
I was told that there was another motor similar to the D336, maybe 360 or 380 or something like that, and this could be that motor also. I know it is one wierd motor 60* V8 with DOHC split heads. It looks like a nightmare on roids. :lol:
A few things to look at, accessory pumps on the flywheel housing and oil coolers.
You might run into issues with those pumps. We ran into that looking to get rid of a D346 once. Seems like it had 5 or 6 pumps back
there, and we couldn't find anything 'up to date' that we could configure that way without being EXPENSIVE.
The later 621's run a 3406 wich is easy to find and will be enough power, but again accessory drives on the back are an issue.
The trans oil cooler is on the engine on those. Available, but pricey as all that stuff is 'industrial' and on a different price base.
Look that stuff over and see if its feasable.
One of the aftermarket parts guys we worked with in Indianapolis turned out to be reasonable enough on parts (and could actually
find 'em) we just rebuilt ours. It's really hard to justify puttin' money in an engine that old. If it winds up you have to go that way and
you want his info, drop me a PM -
I haven't been coming on here much anymore as my BBF projects are all "done", but holy cow, is there any moderators left? I'm trying to help out by reporting spammers as I come back, but wow, there's a TON of them, and it seems like some that I report go unnoticed for days or weeks.