have swapped in overdrive before? itll physically bolt up but there are a few details to work out. the lockup is one issue, I used a kit from TCI http://store.summitracing.com/partdetail.asp?autofilter=1&part=TCI%2D376600&N=700+115&autoview=sku and for the line pressure I used the stock cable, bu this was on a V8 might be different on a inline, but lokars should have a cable you could use or find a cable from a six that was in a car or truck that had a th350 and use that kickdown switch and use that ford linkage kit from edelbrock maybe this one not sure with no pix http://store.summitracing.com/partdetail.asp?autofilter=1&part=EDL%2D8003&N=700+400065+319681+115&autoview=sku
yes. a 250 inline has the same bellhousing bolt pattern etc as a v8. the gm overdrives have a kickdown cable to worry about. if you have some "normal" carb like a holley or a qjet, look at bowtieoverdrives.com for the appropirate cables & brackets. if you don't get it right, you might fry the transmission. you can defintely work this out, just do your homework. ed