right, it makes sense now. most, if not all t4 engine into t1/2 vehicles use some form of upright cooling and do away with the original t4 'suitcase' cooling. there are numerous routes you can go down here and there is an abundance of info/advice/experience on shoptalkforums.com and the type4rum. cheapest method is to make your own parts using a guide like the joe cali nextgen cooling conversion. this basically uses some modified parts; beetle fanhousing, pulleys oil cooler and bits of metal. it's not too difficult, but you need some practical skills/understanding etc. intermediate is using an upright t1 based cooling kit from the likes of sharpbuilt in australia or csp in germany. you can buy all the parts so simply bolt on. another upright option is a dtm (down the middle) cooling kit from jake raby (states). this is a 'everything you need bolt on kit'. final option, and probably most expensive for upright cooling is utilising a porsche fan. this requires some modifications too (engine case machining). the rest not too dissimiliar to a t1 cooling really, pulleys, oil cooler etc). you can buy the fan (porsche) housing from lots of people; sharpbuilt, csp, stateside tuning, l.a. performance and many others. oh, you could also just shoehorn in the t4 lump as it is. but you'd have to cut your rear valance some, and probably end up sticking out the back of the van. fine if you have no sense of taste whatsoever. agian to reiterate; shoptalkforums! everything you will possibly need to know + more is there. it's dedicated to the t4 conversion.
also you imply an '83 engine out of a t25, yeah? these have enclosed breather towers on the engine case (front rhs case). this can prove awkward for some modifications, though not impossible. the preffered case is the, er what pre 83/82? a bay window t4 engine, or 411/412 car. these have an open breather tower and make certain installations very easy. what we are talking about here is the support for the generator on t1 based cooling. open-breathers mean you simply drill some holes and bolt in some plates of metal to provide a base for the alternator suppost bracket. closed-breathers would mean machining the case and probably welding in some billet to support mounting. not impossible, but not as easy, yeah. not so much difference if going the porsche fan route, as it all needs machining anyway.
laters.