Upper Receiver Advise

[65Whelen]

Putting together an Upper, primarily for bench fun. With accuracy in mind what receiver should I get. I'm down to the following choices:

https://www.primaryarms.com/Upper_Receiv...ft55m4.htm

https://www.primaryarms.com/Vltor_MUR_Up...mur-1s.htm

Or, is there something else on the market I'm not aware of. Looking for the heavier, thick walled forged receiver with no forward assist. I would like a billet receivers but they are just a bit out of my price range.

Componets I already have for this build:
18" Rock Creek Barrel
JP Recoil Eliminator
12" MI Gen 2 Handguard
BCM BCG

Also, what would be the best Adjustable Gas Block that will fit under the MI Handguard?