So my FIL is literally on his deathbed, and the one thing he wanted to see was his Datford running again. The Datford is a 1967 Datsun P/U with a build engine/trans out of a 1969 XR7 Cougar, that was then built up. I've had to replace the older than me (And I'm in my 30's ) electric fuel pump with a newer Holley Red unit, the Holley Double Pumper carb on it had a cracked baseplate so I replaced it with an Edelbrock performer as they are what I'm familiar with. It would kinda want to start but would run like ass and quit after about 1-3 seconds while stumbling badly, I was adjusting the timing and went to start it and it backfires with a BOOM the crankcase breather shoots off the engine, hits the hood with enough force to dent the hell out of it, flys accross the garage and into a collection of junk. There was smoke everywhere and my wife came running assuming I had somehow killed myself

But what I'm reading I'm led to assume that this level of crankcase pressure pretty will assures me the engine is blown, but I don't want to give up if that isn't the case. Little help?

For the record if it is blown I'm just going to say I'm an inept mechanic and suck at life, it would really hurt his pride if he knew his baby was shot.

Compression check is in order.
ETA - Sounds like there's a hole in a piston or badly scored cylinder allowing fuel to build up in the crank case. It happened to ignite causing the oil cap cannon.

Pretty much what I was assuming, his shop is a mess and I can't find any tools outside of the standard stuff so I think the "Im a cop not a mechanic!" excuse is the way this is going. Thanks for the assist!

First check firing order (351W's are different than 302's) and timing.

Have you checked fuel pressure at the carb? Are you even running a fuel pressure regulator?  Make sure you are not over pressurizing the fuel and dumping fuel down into the engine.  This could cause a build up of excess fuel that could have ignited off causing the shit storm you described.  
Change the oil if so. It has so much gas now, you will ruin the bearings if run thinned with gas.
As mentioned, check firing order.  Was the distributor removed since it ran last time?  Make sure rotor button is pointing at #1 plug wire at TDC of the compression stroke.
Compression test is a great idea now.

If I could get to the rear 2 plugs on either side and had my tools I'd be happy to do a compression check

According to dad it ran rough and when it ran last, then it wouldn't restart without the stumble and die previously, and then the fuel pump died so he gave up/ran out of money to mess with it. I am curious about the fuel pressure thing though, but from I was read I was led to believe that fuel pump was self regulating? I always just used stock mechanical pumps so this is outside the purview of experience.

Ultimately my wife wants the truck, and being I'm the only one in the family that has a clue on how to work on it it'll be coming home with me. So I'll happy to take and listen to any and all advice on the matter. Thanks everyone!

Those red pumps push a lot of fuel. You only need something like 6psi at the carb.  I would start with fuel pressure and checking compression stroke on #1 at TDC.  Sounds like your distributor just might be out 180 degrees.  Get a fuel pressure gauge and a regulator and do the checks for starters.

Regulator is on the way, wont be next week until I get to work on it again, I'm doubting he will make it that long

Thanks again

Blue pumps push a lot of fuel, not red pumps.  Red pumps are intended to be regulator free.  I seriously doubt that it can push the needle off the seat.  It really does need a compression test.

 

Sorry for the belated update, Dad passed on the 7th, but I had it running on the 5th! (right before he fell asleep and never woke up ) Regulator did the trick. He was soo happy to hear it run, thanks gents.

Sorry to hear that. Glad you got it running for him.

This. You made a dying man happy for the last time - that's a pretty cool thing.

This!
Crankcase ventilation in the older engines is pretty simplistic: vent/breather on one side and a 3/8 or 5/16 vacuum hose attached to a PCV on the other. forced induction engines will make a bit more blow-by, and if its been sitting a while "mysterious" things seem to happen to rings, pistons, seals, carbs, etc.
Check the oil for fuel...
Compression or better yet a Leak-Down test each cylinder.
Check the firing order as it is different and IIRC varies from decades, also are you sure its a "Winsor"?  The 351 Cleveland looks exactly like the 351M/400, the Winsor looks like a 302, and the Boss 302 (or built variants) were essentially 302's with Cleveland heads (think big oval intake ports) where the SBF has small rectangular ports.
Keep at it. its a labor of love.  

That's what he always said it was, and that he pulled it out of the XR7 Cougar it started life in (back in the early 70's). I know old Mopar and Chevy, Fords might as well be European

Neat story. Glad you got it going for him. years ago I helped one of my old employers get his father in laws Henry J  running again before he passed. Flathead six. It was fun just to see the look on his face to hear it run again.

Awesome!

That's awesome!
Sorry to hear about your dad.
Prayers inbound.