This situation does not need to be all that bad. Yes, the space is tight and it is a pain in the a**. But it can be done.
If this were my project, I would just re-plumb this section of your plumbing with PEX, and configure it to match the fittings on the new pump. PEX is easy to work with once you get the hang of it. You can get a set of appropriate tools for about $100. Not chump change, but it could be worse.
There are three options in the PEX world.
uses plastic rings, and the tools are very expensive. Unless you want to re-plumb your house, forget this one.
2. Copper crimp rings.
This is what SMB uses. You will need a tubing cutter, a crimp ring removal tool, and a crimping tool. Total cost: about $100. You can get all of this at Home Depot. Don't get the really cheap stuff. You'll just end up replacing it when it doesn't work. One of the keys here is to get a good tubing cutter. You MUST cut the tubing perfectly square. If you don't, leaks will result.
3. Stainless steel clamp rings.
These are similar to the copper crimp rings, but they use a ratcheting clamp process instead of a squeeze crimp. You will need the same tubing cutter as above. You'll also need a clamp tool. No crimp ring removal tool needed.
I currently use the copper crimp rings, but I wish I had bought tools for the stainless clamp rings instead. For my next job I will probably bite the bullet and get a set of tools for the stainless clamp rings. The crimps require many four letter words in tight spaces. The clamps only require a couple.
1. The fitting shown in your photo has been scarred by your hacksaw. It will likely leak if you try to re-use it. Don't do it.
2. You can also use the "push to fit" (PTF) fittings. The PTF fittings cost about $5.00 a pop, so they aren't cheap, but they are really easy to use--and they can be removed and re-used, which is very cool. They also work very well in tight places--where the clunky crimp tool (and the somewhat less-clunky clamp tool) can face challenges. I'll stick a pic of a water heater bypass system that I installed in an earlier rig at the bottom of this post. It illustrates the use of copper clamp rings in conjunction with PTF fittings.
These are links for Home Depot tools. You can get them other places, as well. Check out the videos that HD provides--they give you the basics. And again--you don't need top-end tools, but get decent ones, or you will be crying into your Cheerios. The stuff in the links would do just fine.
PEX Cutting Tool
SharkBite PEX Pipe Cutter-U701A - The Home Depot
Copper Crimp Ring Removal Tool
SharkBite Copper Crimp Ring Removal Tool-23055 - The Home Depot
Copper Crimp Crimping Tool
SharkBite 1/2 in. and 3/4 in. Dual PEX Copper Crimp Ring Tool-23251 - The Home Depot
Stainless Steel Clamp Tool
SharkBite 3/8 in. - 1 in. PEX Clamp Tool-UC961 - The Home Depot
Push to Fit Fitting Example
SharkBite 1/2 in. Brass Push-to-Connect Coupling-U008LFA - The Home Depot
To avoid crying into your Cheerios, DO NOT GET THIS, no matter how tempted you are to save a few bucks:
SharkBite 3/8 in., 1/2 in. and 3/4 in. PEX Copper Crimp Tool with Integrated Go/No-Go Gauge-23383 - The Home Depot
Good luck! Once you get the hang of working with PEX, it's actually fun. Get some decent tools, then just tear into it and have a good time.
Example of copper clamp rings in conjunction with plastic push to fit fittings: