FYI FORD MustangSteve's Ford Mustang Forum / falcon vs mustang, and gtp40 spark plug

**Posted by val fulesday** 6/23/2025 4:13 PM

what is the difference between the frame rails between frame rails and aprons on early mustang and falcons? lastly any body know the part number for gtp 40 heads using shorty spark plugs?

**Posted by John Ha** 6/25/2025 5:07 AM

Not clear what you're asking about the heads. Do you want the shorty spark plug part number? If so, I believe it's ACC 0526S (ACCEL makes them)

**Posted by val fulesday** 6/27/2025 8:43 PM

i have a 5.0 engine that i bought used that has gtp40 heads. the previous owner had a 3 angle valve job done one the heads plus some other stuff, which i dont recall.. my plan is to install this engine in my 64 falcon which has a 74 model 302w. what i was wondering about is there any difference in as to how wide the frame rails and aprons are as compared to a 65/66 mustang?
one other than one this other engine i am wanting to put in my falcon, i don't know what year it is, and the only number i find is behind the intake manifold which i can't make out due to the poor stamping, but in the lifter galley in the center are three X. are there any other places to look to find any numbers at all ?

**Posted by TKOPerformance** 6/28/2025 5:45 AM

Casting numbers would give you a year and some other information. Look above the oil pan rails and near the starter location.

**Posted by MS** 6/28/2025 5:58 AM

Those Falcons came with 289, which is identical dimensionally to your 5.0. Are you concerned the engine won’t fit in the car?
Pretty sure Bullet Bob helped put one in a Falcon for a friend a few years ago.

The fact your block has the xxx cast into it tells you it is a roller 5.0 from mid 80’s or newer.

The codes you need are above the starter. There will be an engineering number containing 6015 and a date code cast in raised letters newr where the bellhousing bolts on.

**Posted by Bullet Bob** 6/28/2025 6:09 AM

Having been involved in putting a '96ish Exploder 5.0/gt40P heads and 89-93 EEC-IV EFI in a 64 Falcon Vert, I can sat that the frame rails are narrower on the Falcon, but the engine bay seems to be a bit longer (ft to rr). We were going to use HIPO manifolds but there was just no way to make them work. Steering box was in the way also, as I recall. Also, being a convertible, working out dual exhaust that wasn't hanging too low was more than the owner wanted to deal with. Ended up using the stock 260 exh manifolds, cross-over, single exhaust. It runs fine and gets very good mileage, so the single exh didn't seem to bother the engine setup.
If you have a 302 in there now, the 5.0 should be a drop-in. And the present exh system, I believe, will mount to the gt40p heads with minimum foolishness. Like I said, we got em mounted with the stock 260 manifolds .

**Posted by val fulesday** 6/28/2025 10:47 PM

not concerned with pulling what's in the car and installing the other one. I guess what i'm concerned with the most is there a header that I can use, that any one else has used in a 64 falcon with gt40p heads that will clear everything. I'm fairly sure the headers that are on the car won't just bolt on with out some modification. I have fabed up stuff on the car but my welding skills just are not up to the challenge but I do have friends that said they'd do the welding. at 73 it seems to take me considerably longer to get things done,

**Posted by TKOPerformance** 6/29/2025 7:43 AM

The GT40P heads have raised exhaust ports compared to typical E7TE heads, and other older offerings. When people started putting them on 5.0s in Fox cars there were special headers made for P heads so that the rest of the factory exhaust stuff would bolt up. I therefore think your concern is valid.