I have a 80 elk with a 350 tranny and am considering swapping out the 350 for a 700 wondering is it a straight swap or do i need to change crossmember and drive shaft

Yes, you must shorten the driveshaft & modify the crossmember. A200r4 is a direct swap.

I have a 80 elk with a 350 tranny and am considering swapping out the 350 for a 700 wondering is it a straight swap or do i need to change crossmember and drive shaft

you can also get a cross member from G-Force performance

A200r4 is a direct swap.

200-4R uses a different crossmember than a 350. A 1980 frame is lacking one of the frame mounts for a 200-4R crossmember, but it can be welded in.

Here's my 2 cents worth, but I gotta warn you, if you have more money in your checking account than I make in a week ( and that isn't much), or your running a built engine, click the 'back' tab now.
I had a 700R4 behind a 305 in my old '80' (rip ), and then put it behind my daily driver, a 229, while I work on my 81. ( year 2 of a 3 yr project,off frame). In both cases all I did was to open up the trans mount hole on the crossmember, so that it is no longer a hole, but opened up towards the front. Everything else hooks right up, however, If you don't have the wiring for the lock-up, located on the left side, the converter obviously isn't going to lock-up. My 700R4 has been in three cars now and is still do'n fine, with-out lock-up. Kits are available to make it work if your wiring/computer is gone.
As for the driveshaft, I have been using boneyard shafts (after reusing my original front yoke and installing new joints) and have found them for $10.00. When checking for one, ideally a 60 1/2" would be what I'd look for. All I have been able to find were 60". Now, driveshafts can be measured from three places ( weld to weld, overall, and center of yoke to center of yoke. The measurements I gave you were overall length, it makes the job of locating one quicker. And, I gotta tell you, I went thru 3 that were bent, before I got a good one. A driveshaft shop will check it out for a small fee, just have the joints out before you take it there.
Hope this helps, some of us have the means to do things 1st class, and some of us 3rd cabin, but we've all been in the same boat.
And by NO means is this the best way, but it worked for me. The previous replys have excellent advice and you can also do a search from this sites home page for more info. Bob

I will probadly switch over to overdrive someday but my th350 is in good shape so it will not be any time soon. Keep the advice coming.