Replacing shower valve

Hello All, new to the forum and found you at John Bridge's tile forum. I'm in the middle of remodeling my spare bathroom and need to replace the 40yo shower valve with a single handle shower valve.

Details:
The old valve has separate hot and cold water valves and connects from the bottom.

New systems is single handle and connects from the side.

Questions:
1. Since I'm going from bottom connection to side connection do I need an arrestor or is this an as required installation?
2. I need to increase the distance between the hot/cold inlets to make the connection to the side of the new valve. Any ideas on the best way to accomplish this. I was thinking a 45, short length of copper another 45, tubed to a 90 that goes into the new valve???

Yes, you have plenty of room to use 45's and 90's to get you pipes lined up. Millions of showers are installed without hammer arrestors. If your pressure is modest, in the 55 PSI range, it would probably not be a problem.

On the other hand, you have a lot of unsupported piping there which can move around. I also do not see any support on the exisiting valve. I would recomment putting in an approriate brace for the new valve, and since you have room, you could add commercially supplied hammer arrrestors on the hot and cold.

I agree with installing arrestors now while it is open...
Offset the pipe out 6" with 45s, then, instead of turning towards the valve with 90s, use T's...
Into the top solder some 1/2" hammer arresters... (I prefer to solder them on when they are going to be buried...)
If the back side of the wall is a closet, put in a 12X12 or 18X18 access panel. Then you could use threaded in arresters...
If youi do this, just before the T, sweat in a ball valve so you can turn the shower supplies off for service of the arresters and shower cartridge in the future if required...
If you are not going to have an access panel, I suggest spending a few extra bucks and making sure your new valve comes with integral stops...
That way you just have to remove the trim escutcheon and turn off the stops to service it in the future instead of having to turn off the houise and lose water while servicing the valve...

Thanks all for the excellent advice. There are cutoff valves just below the floor in the crawl space (very easy access). They are in good shape and did their job . Got the old valve out and most of the new assembly done. I will have access on the other side of the wall so I bought the threaded arrestors.

valve

a picture of the new valve would have helped. Often they are narrow enough so that street elbows fit to the old risers, unless you got the DIY versions which need male adapters into the threads.