front spring removal help

I'm not sure what you mean by " a tool that bolts on the spring perch", but here's my favorite way to safely remove Mustang front springs. I put the car on jack stands, take off the front wheels, then unbolt the sway bar from the control arms. Then unbolt and remove the shock, as well as the shock tower supports that are inside the wheelwell (tire side) and are held on by 6 bolts per side. This pretty much exposes the whole spring so you can see what's going on in there. Then beg, borrow or buy a spring compressor. I prefer the type that goes inside the spring, since you can compress the spring quickly with and impact gun, reaching down from the top through the shock tower, but any coil spring compressor will work. Once you compress the spring, it easily comes right out, and if you're cutting your springs (I did) or using shorter aftermarket springs, you may not even need the compressor to put them back in. Good luck and be careful!

Leave the perch alone; you only want to compress the spring.

You should be able to rent the tool from an auto parts store. Around here, you can rent these type tools from O'Reilly's or AutoZone. Basically, you pay for the tool, then bring it back for a full refund. Cash, check or card works. Just make sure that when you rent the tool, it has all the pieces there. I once rented a puller and one of the previous renters lost some of the bolts I needed.