Can those valves be installed in 113 heads with stock
seat inserts? And would there be any point in doing
so without moving to larger seat inserts also?

I've been reading and opinions are different. Some say
that this can be done and it's a good upgrade combined with
porting, and other say that LT4 valves (2.00 and 1.56) are
max that can be used with stock seat inserts.

My experience is that the intake can be done, but the exhaust can not be done in the factory seat (1.56" exhaust max). At the point that you are cutting out the factory exhaust seat, you might as well replace the intake with interlocking seats, and then you can go 2.05/1.60. But once you have the new seats, and larger valves, you are really re-working the bowl area, and it tends to be more cost effective to go with a good aftermarket head.

Aftermarket heads have advanced tremendously in the past 20+ years (113 introduced in 1988).
Aaron

Good point Aaron, you can go 2.00/1.56, but the stock castings have their limitations. Depending on budget and hp goals, you will probably be far ahead to go aftermarket heads