Okay, made some pretty significant strides that warrant photography and a novella of an update - (over a month ago since the last one... Jeez, life comes at you sometimes). I've also figured out how to insert photos from and Imgur hosted upload, so while kludgy I get to keep adding photos without deleting the old ones.
The donor Impreza is almost out of my shop - I'll have it hauled off early next week and until then the neighbors are gonna have to deal with it being in the driveway. I've begun cutting away any mounting pieces or sheet metal with bolt holes and mounting bracketry I think I may need. This includes some of the firewall, the access panels for the fuel tank, and most significantly rear shock towers and transmission tunnel. So far I've only completed the removal of the towers, but considering the geometry involved I figured it was probably a good idea to take some time to go about it halfway properly.
Before cutting anything off the body I had to remove the fuel tank and rear subframe. The subframe was quite an interesting proposition, and I managed to do it without disconnecting the rear struts from the knuckles, but that was a shortcut that turned out to probably take more time than what I'd maybe hoped as it required some creative jack and jack stand work. For those following in my footsteps in the future I might recommend taking the time to remove the struts from the knuckles, then replacing the wheels before undoing the (surprisingly few) subframe bolts while supporting the diff and carrier on a low-clearance transmission jack. I had to strain on the bushings while also rolling this on its drums to get everything out from underneath, but without the struts it would have been a much easier proposition to roll it out from under the car. This also being said, this would also be a moot point if I had a lift, which would have made a lot of this much, much easier. Oh well, wishes and fishes and whatnot.
I got the fuel tank out pretty shortly afterward, but with this particular car in this particular locale, all of the rubber and hoses were very, very, very tight and dry on their fittings, so more cutting of tubing than I would have liked had to take place. that being said I'm not sure which tank I'll be using yet, the brat or the impreza, so I'll likely need to reroute fuel lines anyway.
Once I'd given everything with fuel a chance to drain and/or evaporate overnight, I began the dirty, dirty work of actually cutting away the pieces I'd need, beginning with the rear strut towers. (Fire extinguishers nearby, don't you fret)
I'm not sure how much of these towers I'll really be needing, so I decided to just take the whole interior wheel well. To somewhat preserve their geometry I braced them with a few pieces of angle iron tacked into place. I've been considering the difference in width of these cars, and the plan is to use the angle iron to keep everything aligned by cutting out the extra width (to be measured still) somewhere in the middle, then rejoining them with another "bridge" piece of angle and either clamps or tack welds to keep everything nominally aligned while I splice everything else into place. Wish I could say this was my original idea but there's a build thread I found (I think over on NASIOC), where someone doing a similar swap (WRX Sedan of similar year) into a Gen 2 Brat did a similar setup to get the rear suspension Frankensteined in.
Other things to consider:
Part of the reason I got such a good deal on this donor was the rust damage at the rear driver's side (left) strut tower. Going to have to make sure I remove or mitigate all the cancer there somehow so as not to doom my Brat build from the getgo.
Also after looking at the rear subframe some, if I am going to splice it shorter, I'll need to get creative with the linkage and where it mounts. I'm not sure yet if i'll need to shorten the linkage AND the subframe, or if there's a way I can maintain the linkage geometry without running into clearance issues with the differential, all while keeping it under the Brat. Food for thought I suppose, but I'll tackle that problem when I get there. For now I forge on to cut out the transmission tunnel and a few pieces of firewall, as well as take a final pass over to pick off any other scraps I may find useful. Once the Impreza shell is well and truly gone, the Brat goes back up on jackstands so I can start removing the old rear end on that to begin making room for the new rear driveline.
Onto the next steps!