and the 6r trans bolts to a pushrod small block?
I am sure the trans adapter can be welded on....... I am going to say yes, with a good mig setup for aluminum or a TIG.
I mean its just aluminum, not magnesium?
Several of the Ford transmissions I have owned over the years have had the cases or extension housings repaired with nice aluminum welds, not sure why the 4r70w would be any different.
When I ask Brett about running the 6 speed behind our 302/331/347 engines he tells me its not worth the $$$$$ it would take because the gearing is all wrong for the pushrods powerband. I know you said something about running like 3.08 to 3.27 ring and pinions would help?
The thinking here is its best to use the mod engine (2005-2011) along with the 6 speed likely end up being similar $$$ but much better performance?
I am sure you have all of these bases covered, but I love to discuss putting a 6, 8 or 10 speed behind the pushrod would be awesome!!
Thanks for telling me I can weld on the trans extension, I have a spare of that and I'll see about finding a cheap or damaged late model TC to use the front half of that case, to section and weld on.
I am sure you can handle the moderate work it takes to install the 6R80 onto any SBF. Someone makes a front adapter kit for about $700-$750, but the four TC stud extensions look really weak to me for mounting a TC 1/2" farther away from the engine. I saw people on Youtube etc, making a steel plate out of 1/4" and 3/8" steel. The trans bolt pattern is the same, that is, the holes are all there, but on modular engines they use two different ones, and the locating dowels, are where they need to be for a SBF(mounting bolts). So the plate is needed just to mount a starter, to locate it properly for a SBF. So the steel plate needs enough meat to cut 3/8" threads, I think I'd weld a thick quality nut at the holes for the starter bolts. So you arrange the mounting bolts, get the right lengths for those, make the adapter plate, and order a TC with the studs longer to match the new plate.
The trans mount is close to where a 4R mounts, but it needs a little altering also. The TC's bolt directly to the later transmissions, so either you use the late TC and whatever controls them, or make an extension using a late TC front half case, welded to the back part of a 4R trans extension. The shaft I don't know yet how close it is for length or spline count.
The six speed gears are generally like the five speeds, with one lower gear to start with. So the 2nd gear is not far from where the 4R and 5R have their 1st gears. They are a close ratio six speed, get the 1st gear final drive ratio set well for the engine, and it will be great through the whole range of speeds. High gear is still 0.70:1, so a 3.27 gear would have cruising rpm nice and low, under 2000rpm at 70mph.
Late model cars have stock rear gears like 3.15:1 or 3.31:1, most people suggest those two are almost equal in performance for stock or moderate level engines. So for the older cars, I think anything in the 3.08 to 3.27 range would be good, I wouldn't want 3.55's unless the engine was under powered, say 160hp like the OHV 4.0 V6.
For a stock 3.7 in my 4500lbs 99 Limited, the 3.27's might be a good gear, for it might get sold to a friend for mail delivery. For my 98 Black Coal project truck, with big power, the 3.08's would be more than enough. I need to find out how hard those factory front diff gears are to buy.