What is the best service manual for removal/replacment and overhaul of my '98 S70 engine?
I would guess the Volvo manuals are the best. The last I checked there were many manuals for this car that added up to quite a bit of $$$.

Which manual(s) are the best for my purpose of removing, overhauling, and replacing the engine? And where can I get them?

Thank you.

Kenric

P.S. I am still looking for information about the interchange of blocks for this engine. It is non turbo. Will any 850 blocks interchange? They are far more plentiful than S70 blocks.

P.S.S. I am still in desperate need of a replacement block for this engine. Does anyone have an engine with problems, perhaps it had a broken timing belt or head problems, that has a salvagable block?

You might try www.alldatadiy.com. Gonna cost you $25 to see
if this meets the requirements (since you will have to
subscribe) but it seems the cheapest way to get at the factory
documentation. Not as complete as the $1000 set but may be worth
it as a starting point.

The engine page for a 98 includes:

Engine
. .
Technical Service Bulletins
Customer Interest
By Symptom
All Technical Service Bulletins for Engine

. . Description and Operation
General Information
Engine Performance Data

. . Service and Repair
Removal and Installation
Engine Replacement, Transfer of Components
Reconditioning Engine
Sealing Micro-Enclosed Screws

. . Part Explosion

. . Parts and Labor
Engine Assembly
Replace
Overhaul/Rebuild

. . Specifications
Mechanical Specifications
Pressure, Vacuum and Temperature Specifications
Capacity Specifications

. . Application and ID
Product Plate
Identification Number
Engine Serial and Type Numbers

. . Service Precautions
General
Timing Belt and Related Repairs

. . Tools and Equipment
Tools For Engine Service and Repair
Tools For Engine Reconditioning

Why don't you reach out to Scotty Boy who posted a few days ago about wrecking his? His is a T5 so the retrofit would be more extensive.