Have a look at the FAQ's to see a procedure for T-belt change.

https://www.brickboard.com/FAQ/700-900/EngineSealsBeltsVent.htm#960TimingBeltChange

There are only two pulleys with bearings in the T-belt route: the idler and the tensioner. It's relatively cheap insurance to install new items.

I don't know if there is a "Volvo kit" for the T-belt components...the one I bought was put together with OE Volvo parts by internet parts house FCPGroton.

While you are in there, replace the serpentine belt unless it has low miles. Cheap and easy, and there is at least one story around here about a serpentine belt failure getting into the T-belt assembly and wrecking it and the engine. Memorize your serpentine belt routing. Volvo changed it at one point and the belts now sold are too long for the previous routing....which is still being shown as correct on some web pages.

I used NGK platinum plugs (BKR6EGP) in my S90. They outlasted the OE Volvo plugs and were still running fine when I sold the car. If you pull the plugs to move the crank to align the cam pulleys with their marks, reinstall the plugs immediately after. This may help keep the crank from moving as you wrestle the new T-belt into place on the crank pulley.
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Bob: Son's XC70, my 83 244DL, 89 745 (Chev LT-1 V8), 98 S90 (recently sold) and 2010 XC60. Also '77 MGB and four old motorcycles