421
Type approved 1 May 1967, powered by two Continental GTSIO-520-Ds of 375 hp (280 kW) each, maximum takeoff weight 6,800 lb (3,084 kg).
200 built.

421A
Type approved 19 November 1968, powered by two Continental GTSIO-520-Ds of 375 hp (280 kW) each, maximum takeoff weight 6,840 lb (3,103 kg).
158 built.

421B Golden Eagle/Executive Commuter
Eight-seat light passenger transport aircraft.
Type approved 28 April 1970, powered by two Continental GTSIO-520-Hs of 375 hp (280 kW) each, maximum takeoff weight 7,250 lb (3,289 kg), later models 7,450 lb (3,379 kg).
699 built.

421C Golden Eagle/Executive Commuter
Model with new wing and landing gear.
Type approved 28 October 1975, powered by two Continental GTSIO-520-Ls or Continental GTSIO-520-Ns of 375 hp (280 kW) each, maximum takeoff weight 7,450 lb (3,379 kg).
859 built.

Riley Turbine Rocket 421
Conversion of Cessna 421 aircraft by fitting two Lycoming LTP101 turboprop engines.
Formal designation R421BL and R421CL for conversions of 421B and C respectively.

Riley Turbine Eagle 421
Conversion of Cessna 421C aircraft by fitting two 750hp Pratt & Whitney Canada PT6A-135 turboprop engines.
Formal designation R421CP.

Excalibur 421
Re-engined 421C with Pratt & Whitney Canada PT6A-135A or PT6A-112 turboprops, supplemental type certificate held by Excalibur 421 LLC of Paso Robles, California.
In 2013 it was announced that Aviation Alliance are acting as program managers for the Excalibur 421 upgrade programme.

Advanced Aircraft Regent 1500
Production of the Riley Turbine Eagle 421 conversion by Advanced Aircraft Corporation.
421
Type approved 1 May 1967, powered by two Continental GTSIO-520-Ds of 375 hp (280 kW) each, maximum takeoff weight 6,800 lb (3,084 kg). 200 built.
421A
Type approved 19 November 1968, powered by two Continental GTSIO-520-Ds of 375 hp (280 kW) each, maximum takeoff weight 6,840 lb (3,103 kg). 158 built.
421B Golden Eagle/Executive Commuter
Eight-seat light passenger transport aircraft. Type approved 28 April 1970, powered by two Continental GTSIO-520-Hs of 375 hp (280 kW) each, maximum takeoff weight 7,250 lb (3,289 kg), later models 7,450 lb (3,379 kg). 699 built.
421C Golden Eagle/Executive Commuter
Model with new wing and landing gear. Type approved 28 October 1975, powered by two Continental GTSIO-520-Ls or Continental GTSIO-520-Ns of 375 hp (280 kW) each, maximum takeoff weight 7,450 lb (3,379 kg). 859 built.
Riley Turbine Rocket 421
Conversion of Cessna 421 aircraft by fitting two Lycoming LTP101 turboprop engines. Formal designation R421BL and R421CL for conversions of 421B and C respectively.
Riley Turbine Eagle 421
Conversion of Cessna 421C aircraft by fitting two 750hp Pratt & Whitney Canada PT6A-135 turboprop engines. Formal designation R421CP.
Excalibur 421
Re-engined 421C with Pratt & Whitney Canada PT6A-135A or PT6A-112 turboprops, supplemental type certificate held by Excalibur 421 LLC of Paso Robles, California. In 2013 it was announced that Aviation Alliance are acting as program managers for the Excalibur 421 upgrade programme.
Advanced Aircraft Regent 1500
Production of the Riley Turbine Eagle 421 conversion by Advanced Aircraft Corporation.
Cessna 421