The R4s had quite a bit of pumping capacity (163-180cc/rev, thereabouts), more than the Sandens (7cyl Sanden ~155cc/rev), akin to the OE HT6 (165cc/rev), and less than 10-cyl 4-Seasons HT6 model (210cc/rev).
GM used the R4 on the dual-evap Suburbans, and your cooling needs are less... but you are in TX.
As for the R4 retrofit scroll compressors, the GPD 6511351 specs say "180cc", I assume that's 180cc/rev.
The scroll compressor is said to perform best at high speed (meaning not at engine idle), so there's that.
Finally, there's likely a separate discussion to be had about which orifice tube you should use with your setup.
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