First, buy this book:
http://falconperformance.sundog.net/Then, check out the small 6 forum at
http://www.fordsix.comThe short answer is that a 200 will fit anywhere a 170 will but there are some bellhousing issues on one that early and I'm not sure which years of 200 fit your tranny; the guys on that forum will know. If the trans doesn't matter, you're golden with a later 200, which adapts nicely to a T-5.
A little ingenuity and you can put a 250 almost anywhere the 170 fits but the tranny will not bolt up and you may need to do some oil pan surgery. The 250 block is taller so there may be some hood issues as well.
There are a bunch of speed parts for the 144/170/200I6 including a very trick aluminum head available from
http://www.classicinlines.com/