While this question might be best aimed at Fantech, who will likely answer their 'phone, here are a few thoughts:

The range hood for a 48-inch range should have at least 8 square feet of entrance aperture, with more being better, depending on the physical situation. At 8 square feet, the volumetric flow rate at full power should be 720 CFM. A blower that can yield this at the pressure losses of a proper duct with a proper make-up air (MUA) system supporting it would likely need to be rated at a bit over 1000 CFM (zero static pressure value).

720 CFM actual through an 8-inch duct yields a velocity of 2063 ft/s. This is at the high end of of the recommended duct velocity range of 1000 to 2000 ft/s. It will have a significant pressure loss if the duct length is longish, as the description implies. It seems likely, when accounting for baffle pressure loss and potential imperfect MUA, that the zero static pressure rating of the blower may need to be higher than 1000 CFM to actually achieve 720 CFM.

To get to the actual question, when a blower is slightly gagged in its flow rate, it moves less air (see the Fantech fan curves -- I think they are in tabular form -- for flow vs. pressure loss). When it moves less air, it does less work, so harm is unlikely.

In the limit, where the pressure loss gets to 2 inches or whatever for the particular blower, the blower moves very little air. (If there were no air movement, there would be no pressure loss.) Note that the zero flow rate pressure loss value is a tiny fraction of the actual air pressure, so blower over-speeding seems unlikely, but this is a question better asked of Fantech.

tl;dr: The concept should work, probably better than an 8-inch FKD, but it will work marginally, at best, because the hood size demands a higher flow than one may get, depending on the hood.

Use of a blower with a better flow rate at higher static pressures may be a better choice. Fantech may have options. Expect more noise. Use a Fantech silencer if it can be installed between hood and blower. Consider reconsidering your "not an option."

Also, consider reconsidering the size of the range you want to use in an architecture that is not consistent with its needs.

Last, marginal ventilation is better than no ventilation, so I don't want to discourage trying for the best that fits.

Sorry but no one needs a 48” range and the MUA and the venting will cost more than the range I run a catering biz with a 36” and yes you will need 10” duct work and when the ducting gets that long you will need more than 1000CFM that ducting has to go trhough your roof too. How will your hood you have now be big enough for the new insert. ?

Thanks so much for the responses. Sounds like I need to talk to Fantech to see if there might be other options. To answer the question about the range, we need a second oven, so will have to go to a 48" range. No space for a wall oven. We are just going to rebuild the cabinets around the range. We won't use if for indoor grilling and in all honesty, hardly ever use the current range hood. I don't want to put a Ferrari engine in a Yugo when it is still going to run like a Yugo no matter the engine. And I might be happy with the Yuog being a Yugo because it is better than nothing.