You need flywheel for '89+ 5-spd.

Starting in '89 Volvo 240s used LH2.4 and LH3.1 ignition systems.
The spark timing is driven off the flywheel, read by a crank position sensor located at the back of the head/block.
Hopefully you already got the 5-speed version of the flywheel for '89-forward cars. If not you'll have to get it.

So far as I know, all the auto-trans cars '89+ used LH2.4 ignition.
Most if not all the 5-speeds used LH3.1 which was very similar to the LH2.4.
Any '89+ 5-speeds not using LH3.1 would have used LH2.4 ignition.
You can keep your LH2.4 ignition, no need to change it all over to 3.1.

I don't think it makes a difference whether you get a flywheel from an LH3.1 or LH2.4 5-speed car - but you should double check just to be sure. You can't use a flywheel from auto trans, and you can't use one from a pre-'89 5-speed.
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Sven: '89 245 NA, 951 ECU, expanded air dam, forward belly pan reaches oem belly pan, airbox heater upgraded, E-fan, 205/65-15 at 50 psi, IPD sways, no a/c-p/s belt, E-Codes, amber front corner reflectors, aero front face, quad horns, tach, small clock.