I have a Gen-1 receiver I built on an Italian kit. They sold bare receivers back then (8-10 years ago?) It has given me no trouble and worked well from the start and assembled fine.
I think the difference is that Gen-2 is forged billet and Gen-1 is cast. Generally people prize forgings vs cast as they should have superior strength,
You could convert a Garand receiver however they are hardened steel and require a machinist with carbide tooling willing to cut it - Schuufs had a service for this - It is not a typical DIY Smith project unless you are familiar with machining.
Garand prices from CMP are not as inexpensive as they used to be, last time I was at a CMP store, many Rack Grades were heavily pitted receivers, but still serviceable - not sure if they are better but they are a GI forged part that otherwise met dimensional specs.