This "simple" (Ha!) job can be a challenge, even for the experienced. Frankly, I wouldn't advise it, assuming it's your daily driver and you can't afford any unexpected problems on a simple job.

But if you do go at it, and manage not to round off the fitting nut, or a frozen fitting nut doesn't cause you to twist and break off the relatively soft copper alloy line, here's a tip to keep from fluid from draining while the line is open...

>>You can prevent Master Cylinder Fluid Loss from any/all open line(s) by blocking the brake pedal depressed. ( It only takes an inch or two on the pre-ABS 240s.) The MC piston seals will block off the resevoir ports. Disconnect the battery to keep brake lights off.

I've been using this on '80s 240s for about 10 years now—ever since I learned it from an independent Volvo specialist. I made a wooden prop that hooks to the bottom edge of the pedal and bears against the 240 seat adjuster bar. It's handy for checking brake lights too.<<

The line fitting takes a 11mm or 7/16" flare wrench
The mounting bolts are 17mm. I use a box end wrench and a copper hammer.
The bleeder is 8mm or 5/16", but some rebuilts are 1/4".

Dont apply slow force to the fitting nut or bleeder. Shock the wrench gently with a small hammer. If/when you see movement, use the Kroil or P-Blaster as you work back & forth. But don't expect too much from soaking ahead of time.

--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.