I modified my Brownell's bench block tool to fit low profile gas blocks for this very purpose.
You can also secure the gas block in a vice with inserts, and tap the roll pin in that way to get it started.
The most critical part of installing the gas block, gas tube, and roll pin is aligning the gas tube correctly to ensure no clipping of the carrier key. This is the most overlooked operation of gas block installation, along with mis-alignment along the longitudinal axis (back-to-front) with the gas port.
The other most overlooked aspect of gas block installation is incorrect gas block ID relative to the barrel's OD around the gas port area.
Competent and experienced manufacturers are able to spec their gas blocks to have an interference fit for a right gas seal, whereas the after market caters to ease of assembly to DIY types who lack proper tools for an interference fit. The end result is a gas block with a gap between the journal and ID, allowing gas leakage and resulting short-stroke FTExtract or FTFeed malfunctions.
The TDP calls for a tight gas block fit to the barrel and the big manufacturers that know what they're doing have fixtures in place to set up the operation correctly and easily.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com