i have an OEM bellhousing to mate a C4 to a 351M, 400, 429, or 460 - so i know at some point in time, ford put a C4 behind one of the big-block bolt pattern engines. these bellhousings are somewhat rare.

the top two engine side bolts are about 7-3/4" apart
the transmission side is mostly circular 10-3/4" diameter, except the bottom is an irregular shape. there are 3 bolts in an arc across the top, and 1 on each side at the bottom. the bolts go in through the bellhousing (tranny must be threaded).
the whole thing is covered in grime, except for the flange where the tranny was bolted on. on that surface there is a fomoco logo, and "RF-D50P-7976-BA CFC 75 E"

for comparison, the bellhousing on the FMX that came off my 351W has the top two engine side bolts about 5-1/8" apart, and the transmission side is rectangular (at least the part that i can see without moving heavy things) where the iron FMX bolts on with a bolt in each top corner. the bolts go in through tabs on the outside of the tranny (bellhousing is threaded).

somewhere on the web i saw a list of C4 bellhousings. there were about a dozen different casting numbers, and only one was the big-block pattern. i think the number was different from mine, but pretty close.

 

actually, i am of the opposite thinking. if you are going to "drive" is more often than not and do a few spot runs(racing), then i would sat 2100-2400. i would also keep the gears or go to a 3.43 or 3.5 max. I have a friend that has 3.43 gears in his 400sbc 73 camaro, he is pretty fast and can drive it a bit as well. he run like a 11.5 @135 or so in the 1/4.

 

[updated:LAST EDITED ON 16-Aug-02 AT 12:54 PM (EST)]part of reason for running those gears in the camaro may be BECAUSE it is that fast - if he is crossing the line at 135mph, he might redline the motor before the finish with 4.11's or even 3.73's - depends on how tall the tires are. and if he has trouble hooking it up with that ratio, then lower gearing would only make the wheelspin worse!

another thing to consider is that a 70's ranchero is about 1000 pounds heavier than a '69 cougar or a '73 camaro. not only do you need the extra torque from lower gears to get the thing moving, but to make it fast takes a lot more power, which means a more radical build (cam, intake, etc.) which means you won't have as much low rpm power, so you'll need more stall and gears.

as far as streetability - my ranchero came from the factory with the 3.89 gears AND a 120mph speedometer. i once buried the speedo pointer (135 or so) and still had some revs left in the bag, but even if i was on the autobahn or an arizona highway, i would NOT go at that speed for anything more than a short burst. but cut that speed and those revs in half, and it would be good to go.

my thinking is this: if i cross the finish in the 1/4 doing 120 at 6000 rpm, then i can go 60 at 3000 rpm. while that wouldn't be a GOOD setup for highway driving, it would still be OK to drive an hour or so to the track, or for cruising over to the local hangout on saturday night and making a few trips up and down the main drag. i don't know what ratio that would be (maybe 4.11 to 4.56 with 28" tires?) but it would definately be lower (higher number) than the 3.89's - i went about 70 at 3000.

basically, to run the best possible ET's, your trap speed should be your TOP speed - you're about to redline your top gear. but that's usually going to mean that your highway revs will be too high to move along at a good clip for a long trip, so there has to be some compromise. to make matters worse, most people (me included!) who race a daily driver have slicks that are taller than their street tires. the shortest slicks are 26", which is much taller than the low-profile street tires on most mustangs and camaros. thank god for overdrive!

of course, when i put those same slicks on the sport-trac, they are much shorter than the stock tires, whick works great! same deal on lightnings to... i don't know what tires i'll end up with on the reborn ranchero - just have to see what fits and how fast it will go!

 

see that is why im a little off, having been road racing i found gearing is a lot different than driving in a straight line. for toadays gas prices, its a 3.0 and aod for me. if i raced it a bit id max it a 3.50.

there is nothing like racing a vette at 150+ mph and asking him if thats all you got. yes i have done some silly things.