Have parts for PI swap, should I check compression before install?

Is there any reason to believe the bottom end isn't in good shape? Unless you have issues, like loss of power, smoking, or a knock, I am sure it is doing just fine. The bottom ends on these engine are relatively stout, and can take about 425rwhp (under 6500rpm) without a problem. Your sub 300hp head combo won't cause it to break a sweat even.

The only thing that concerns me is that the engine hasn't been driven hard. You occasionally need to blow out the carbon. My 97GT goes WOT everyday, and it is still going strong at 192k.

If the engine pulls decent vacuum, doesn't burn copious amounts of oil and runs well I'm sure it's fine.

If your PI "swap" includes the heads then you can do a visual inspection of the cylinder walls with the heads off. You can check for scoring, the presence of a ridge (indicating bore wear), the extent of any glaze. If you have a bore gauge you can even get a general idea of bore condition by taking a couple of measurements with the pistons at BDC.

BTW, I personally don't subscribe to the notion of there being a need for periodically "blowing the carbon out." Modern EFI engines with closed loop feedback run very cleanly. The accuracy of fuel delivery is one the of the reasons engines last so long nowadays: they don't wash down cylinder bores with excess gas and contaminate the oil like their carbureted forebears.