I've got a 78 Bronco that I've finally got a chance to start working on after purchasing it 4 years ago but I'm wondering if I should put the good parts off it on to a 1979 400 block to avoid any possible issues. I've heard stories, as I'm sure you all have about the '77 and earlier "M" blocks and block cracking so I would like to know what year block I have.
Next to the starter it says: D7TE-A2B
By the oil pressure switch it just says: 717 with the MCC for "Michigan"
All the other 351M and 400's I've seen have 4-digit castings with letters and numbers but this clearly only has "717".
Anyway, I'd appreciate any help to finding out if this block is good to keep because time is hard to come by for me and this engine already has had lots of mods done to it before I bought it so I hope it's a keeper.
In case you were wondering what's been done to it the list includes:
-351M block with 400 crank and pistons
-Bored .030 over to 408
-Less than 20,000 on since rebuild
-Ported, polished, and port matched 1970 4V Cleveland heads
-Edelbrock intake
-Holley 670 Truck Avenger Carb
-MSD ignition
-Non-retarded timing gear (unknown brand)
-Custom ground camshaft (real nice idle!)
The guy was out of work for 9 months and needed money so I bought the truck for $750 and had the tires sold the same day for $700 so I only paid $50 for it and the guy told me he put around $3000 in the engine alone. A local engine shop built it for him. They do most all the engines for our local dirt-track guys and the shop is known for building amazing engines so I trust the work just not the block. Anway, I'm done rambling, let me know what you guys find out about this block.

 

The letter is the first year of the decade (C=60, D=70, etc.) the number is the year; D7=77.

So your block was made in 77.

 

My D7 block held up fine to a lot of abuse. Ran straight water for a while as well and never burned a drop of coolant, ever.

I think I got lucky.. I can't imagine the first redesigned block suddenly got a D8 stamp, there has to be some spill-over from 77s or into 78s, I think prior is more likely because of my experience with my D7.. being that yours is a 78 truck, you probably have a late 77 motor and it's probably fine.

I also wonder if it's more in the urban myth catagory as I've never seen or heard of one of these infamous water jacket failures first hand, it's always "i once knew a guy who knew a guy" or some tech article that mentions going straight for a late 78 or 79 because of the weak water jacket/weak block.

 

Yeah I know what you are saying about the water jacket issue. I've never met anyone who has had that problem and between my friends and I, we have owned dozens of 351M's and 400's and worked on many others for random guys and this still was never what the issue turned out to be once we were inside the engine. The most common problems I've actually seen with these engines are bent pushrods and broken valve springs due to people incorrectly trying to fix the retarded timing problem these engines had from the factory. I have a so-called "bad block" year 351M from 1976 in my early 1977 F250 and it is still running fine. This truck has been in the family for decades and has close to 400K original miles(odometer stopped at 320K) and the block is still fine.
I should just go with what I know from experience and not let a bunch of internet gossip sway me from enjoying the sweet engine I have under the hood!

 

D7TE-6015-A2B is the 351M/400 block casting number for 1977/79 F100/350's & 1978/79 Bronco's.

Passenger Car 351M's and 400's have different block casting numbers.

351M: 1975/79 FoMoCo Passenger Cars / 1977/79 F100/350 / 1978/82 Bronco / 1980/82 F150/350 & Econoline.

400: 1971/79 FoMoCo Passenger Cars / 1977/79 F100/350 / 1978/82 Bronco / 1980/82 F150/350 & Econoline.

1976/78 351M's & 400's were very prone to cracking cylinder heads.

Some were replaced under warranty (2 years, 24,000 miles, whichever occurred first). Some peeps had to pay, and...

The total cost for parts & labor was $700.00 .. a lotta money back then.