Reddit mentions of Chevrolet S10 Truck V8 Conversion Manual

See this reference, page 6 under "Tools Required":

>Welding or cutting, in most instances, is not required; however, there are variations in different vehicles that may require the use of a welder or cutting torch.

Additionally, page 8 under "Body Lifts":

>A body lift is not required on both the 2WD & 4WD versions. However, we have found that a body lift greatly increases additional engine, transmission tunnel & hood clearance. This, therefore, reduces the amount of firewall and floor pan modifications. Usually a 2” body lift is adequate in helping to alleviate these clearance problems.

So, looks like you might be able do it without any cutting or welding. That whole PDF looks like a good read for someone going to attempt the swap.

Looks like there's several places that sell swap kits for putting a V8 in an S10, and here looks like good reference material for the swap, or might not be a bad idea to buy it to see what you'd be getting into.