Only two issues. Which we first often discussed often here and again over at Four Eyed Pride on a regular basis.
1.The carry over of the Pinto/Mustang II steering rack created the need for worlds oddest double hump sump,
and
2. they engine bay depth is limited for tall 250 and 240/300 sixes. But if you can fit a 300 or 460 with a little massaging, then any things doable.
viewtopic.php?p=47585
That mid mounted "under cross member steering rack" means you have to create a double hump Oil pan for the Fox I6 250 conversion. This has always been a little bit hard, but they do make 351W, 335(Cleveland based 351c, 351m, 400) and 385(Lima Big Block 370/429/460) pans, so axing up a stock 3.3Fox or Fox body 2.3Lima/3.8 Essex or Windsor 255/302 pan and mating it to a 250 pan rail isn't an issue. Jack showed the red 250 tri power conversion in the early days back from an 80's conversion they did, all sorts of trick dual out headers, home made sumps and welded on tri power triple singles...
Cowl height on the Fox Mustangs is, so you have to use that aftermarket Mustang hood, or 1979-1984 hood bulge used as a hangover from the 1979 to 1981 Mustang Cobra era or Fox Capri 79-85 hood bulges make enough space to clear a 1-bbl, 2-bbl or tri power carb set up on a 250. The other guys on their Box top Fairmonts and Zephyrs just make a carb hood bulge.
The Fox body has a mountian of space width and length wise, but is just a little bit compromised in the depth as Dearborn tried darn hard to thin down the cowl 1" on the Fox Mustangs and Capris compared to the Fox sedans.
Here is a triple carbed 250 engine in a Fox Mustang back from the 80's by Jack Collins. It has a split exhast, early Falcon linkage, and welded on intake adaptor. Doing a triple carb install on a 250 has at least five problems to overcome which I'll detail below, but you get the general idea. And the results are always stunning for power if you follow the leading lights, see Falcon Sedan Delivery's old 65 Mustang (Drag car only) 250 Six + goodies. A Fox Capri or Mustang with the optional 1981 onwards 3.08:1 7.5" limited slip diff can weigh in as little as 2622 pounds with the 385 pound six, only 85 pounds heavier with a low mount SROD . Thats 2707 pounds on a 1981 3.3 4-speed.
viewtopic.php?f=40&t=41798&p=502631#p502631
and
http://www.fordsix.com/forum/viewtopic. ... 87&start=0

The Fox bodies and post 1971 I6 Fords have minor issues with linkage, emissions, kickdown and transmission types which are
very poorly understood. In addition, Ford continued 170/200 and 250 capacity developments to meet 70's to 83 emmissions and different Mavrick, Early Bronco Granada, Fat Stang and Fox body types changed everything carb, kickdown and accessory drive and air cleaner around almost every year, so getting matched parts is something of a lottery. Easy when you know, a bit hard if you don't ask.
The best option on a 250 swap dollar for dollar basis is definately the triple carb Offenhauser or Edelbrock flat top log adaptor, but hooking those old tri power set ups create five often insurmountable catches on Fox bodies:-
1. Each require the old style Falcon Six passenger side linkage which
2. deep sixes the prospect of using the stock A/C pump,
3 the stock EGR valve needs to be removed and
4. there a no stock emissions certified carbs to use.
5. If auto, then the stock kickdown rod on C3 and C4/C5 3.3 sixes then become a non runner unless you use some Ford Six smarts.
(The kickdown rod used on all auto 170/200/250 engine I6's post 1971 is impossible to use on a triple carb conversion, due to its possition right where the back carb goes).
You need to be aware that the stock aftermarket triple carb set up uses either
1.the three new 34 ICH Weber 1-bbl carbs in 1.142" venturi for 138 cfm or 414 cfm at 1.5" Hg, enough to flow 180 to 200 hp all up with the outer carbs staged to come in at 2/3rds throttle
See
http://fordsix.com/forum/viewtopic.php?t=64712
See
viewtopic.php?t=64712
or
2. the slightly better flowing big bore stock Ford I6 production carb versions with
2 x Outer Holley 1904/1908/1909 125/130/150/170 cfm in 1.352" venturi and
1x inner Autolite 1100/1101( or Holley 1940/Motorcraft branded) carbs, 131 cfm 1.20", 149 cfm 1.29" venturi.
For further reading, see
http://vb.foureyedpride.com/showthread. ... 200cid-I-6