sure. I put a replacement crankset (Sugino Impel 150) on a Trek 930 last week; I was easily able to find the spindle length on Bikepedia and order a replacement set that dropped right in without needing the adjust the FD.
For the 800 though, I can't determine the year of the bike to be able to find the spindle length. On Bikepedia, Isee more than one spindle length given for 800s (113, 116). For replacement cranks, I see a models meant for 110/113 and also 122. Thinking the 113 should work, although I thought I throw it out to the experts for your insights.
This is for a repeat customer who was comparison shopping and was not willing to leave the bike. As I said I should have at least gotten the serial number to be able to narrow it down a little.
87 Trek 560EX * Sanwa SS * 80s Schwinn Traveler SS/FG * 90s Univega Via Activa 300 * 90s Trek 830 * 2011 Fuji Sagres 2.0