An internet search produces little info, seems to be mostly a Marine Engine, but turns up in a GenSet now and again, which is my interest. Looks to be a 6 cyl from the 1970's. Any input on reliability and specifications would be appreciated. Also, opinions on dollar value.

That was a pretty popular over the road truck engine & was called a 1674 in the truck but was the same basic engine as the D334. They were a pretty reliable engine but was not the HD engine that the 1693 & the 3406 was (is) of 893 cu.in. displacement.As a truck engine they were at 2200 RPMs 270HP and are 4 3/4" bore & 6" stroke with 638 cu.in. displacement, same for the industrial. They were used in other industrial applications for whatever the customer needed it for besides as a Gen. set power plant.Off hand I don,t have the HP ratings for the industrial engines.

SJ has it right again, the D334 was around 270hp as an indutrial engine, I saw a few mounted in crushing and screening plant, 330hp as a high performance marine engine. strangely enough, its sister, the D336 V8 was a 4.5" bore unit.
Its a money pit if you have any major problems being a twin overhead cam unit, but very reliable if it has not done too many hours and previous spanner monkeys have not done too much damage.

Yes there were quite a few of them around here & they also were a truck engine the 1676 & we called them a Clatterpillar as they were a pretty noisy engine with the OHC set up where the D334 - 1674 was a much quieter engine.I had a trucker come in the shop one time with low power in a 1674 & he had stopped cross country about three times to no avail & one dealer even put a new turbo on but didn,t help. He spent about $2,000 & still no power so he told me & the first thing I did was check the air fuel ratio control & sure enough the diaphragm was blown so I put a new one in at the charge of $1.75 at that time & a few minutes work & power was back up to normal on a road test up a mountain grade there by the shop.I had seen dozens of them blown so was almost sure that was his trouble & it was.

We're still getting engineers caught out by bust diaphragms today SJ, we recently had a 3408 engine blowing smoke rings for this reason, work that one out, I'll tell you later..

We also called the D336/1676 a 'Clatterpillar', I arrived fresh on an overseas job with 3 other Cat engineers, going to work in the Land-Rover on the first day, with the Service Manager, we overtook an Oshkosh with the familiar clatter. 'What the *&@$ engine makes that noise?' said my buddy. 'A Caterpillar' replied our service manger!

Catsilver, I made up a simple testing device to check the air ratio units on the truck or tractor just by taking the boost line off & with an air regulator & air supply line would see if it held air or not & if bad it would of course by-pass in it.You could only use the amount of air pressure for whatever the boost was at it,s peak HP & if I rebuilt one I,d check to make sure it was working correctly after I installed it back on the engine if it was in the shop.I also had a unit made up to test them on the bench & used an old bracket from the gov. where the unit bolts to & had a base welded on it so it was self standing.I made up a lot of gadgets to make work a little easier and find problems in a hurry.