basically yep!!

i cant be 100% sure cos its a job ive never done - ive swapped a 4x4 dohc sierra to 2wd and that was dead easy so i cant see you having any problems, there may be little differences like - the camshaft etc but i doubt very much it would cause any problems - also i think the sierras are 120bhp and the trasnits are 110bhp - something like thats but i'd guess by swapping the injection over yo will lower the spec of the sierra engine, but if you have a look at the sierra engine aside yours you will see what i mean all the pipes are in different places ect. would certainly make it an easyer job keeping the tranny injection.
i once thought the sierrra injection would not fit in the transit - i thought it would foul the servo but ive seen a van with it in so it will go in.