I've done it on a 1990 240... pretty much the same. Should be a chart under the hood.

Very few vacuum lines on these cars. A handful at most. Just replace what you see, the thin stuff is everywhere except one of the lines to the charcoal canister (which should be under the air box in the 740). The IPD stuff goes over metal fittings OK, but I found it a little tight on the plastic fittings (like the flame trap and charcoal canister).

A razor is fine to cut it with, or utility scissors. Doesn't need to be perfect.

I'd replace everything except the nylon line for the MAP sensor (assuming your '90 is Regina). The nylon lines last forever unless a mouse eats them (happened on our '91 740).

Good luck!
-Ryan
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Athens, Ohio
1987 245 DL 314k, Dog-mobile
1990 245 DL 134k M47, E-codes, GT Sway Bars
1991 745 GL 300k, Regina, 23/21mm Turbo Sway Bars
Buckeye Volvo Club