So one of my last threads was on what to use to build a new 351W block for my '94 F-150. I recently purchased some GT40P heads at a swap meet for a steal. I also have a co-worker giving me a 351W engine from the late '70s to early '80s. I am aware that the older 351 has a flat tappet cam and my truck has a roller cam.
My questions are what will I have to do to the new heads to make them fit and what are the differences in the older block and my block?

 

Most (all?) GT40P heads have 7/16 bolt holes. They'll need to be drilled to fit the 351W 1/2 head bolts. If I remember right you take them to 0.530", not exactly 0.500". I did it on a drill press, though that isn't really the right way because unlike a mill you have a lot less control on holding center. I didn't have any real trouble. My advice if doing this on a drill press is do not step-wise increase the hole size. Go straight to the final size (17/32") and the hole center shouldn't be so hard to maintain.

The flat tappet block is fine. You can either run a flat tappet cam & lifters or you can run a roller cam with a set of link-bar style roller lifters. The last option is to run a reduced base circle roller camshaft with roller lifters but I think cam selection is very limited & there's the inherent issues of running a reduced diameter cam lobe. Depending on budget, I'd either do flat tappet or link bar and not even consider the reduced base circle cams.

The other difference in the block may be the rear main seal. I know older 351W used a two piece rear main seal and the newer blocks used a one piece main.

To the best of my knowledge that is it on block differences. But I certainly may not be aware of something else.

GT40P heads do pose a potential for spark plug to header clearance issues due to the spark plug angle (part of the reason these out perform standard GT40 heads) but if you use long tubes it likely won't be a big problem.

 

Thanks for the feedback.
The only issue I found would be the long tube headers. I would think that long tubes would be a little more difficult to route with my transfer case in the way. I'll look at short headers that will (hopefully) fit and go with long tubes if I have to.
And would the spark plugs be the same part number on the stock heads as the GT40P heads?

 

You'll want to use long tubes....the shortys will be in the way of spark plug boots. The y pipe can be dabbed with ease in front of the trans crossmember so as never to even deal with the t case

 

No the plugs are different from what the E7 heads use. Get plugs for a 97-00' 5.0L Explorer.

I ran 2.5" tube along each side of the trans, driver side tube goes over the cross member, makes a 90° bend to go under the front of transfer case. Then another 90° bend to be parallel to the passenger side tube, where it feeds into a Y pipe, and into the muffler. I thought about crossing over forward of the trans cross member but wanted as much ground clearance as possible.

Shorties will probably not fit unless they're GT40P specific.

 

Ok, looking now I may have found shorty headers specifically for the GT40P heads. Going that route seems a little easier to me.
Now for the intake manifold. There are a couple different configurations for one I have no idea which one to go with.

 

I'm not sure that I know of a set of shorties that will fit gt40p