G.P. Revolver 70" specs
Glow Power-
Engine .61-.75 (10-12.5 cc) two stroke OR .81-.91 (13.5-15 cc) four
stroke with Pitts type muffler OR
Electric Power-
Motor:*Outrunner brushless,*GPMG4740*with Motor Mount,*GPMG1260*and
60A Brushless ESC,*GPMM1850
Battery:*Two 3200mAh 11.1V LiPo with Deans Universal 2 to 1 adapter
Battery Charger:*LiPo compatible,*GPMM3015
Cell Balancer:*GPMM3160
Propeller:*Glow, size depending on selected engine
Electric, 15x7E (APCQ1830)
Misc. Items:*Building and field equipment.
Wingspan:*70" (1780mm)
Wing Area:*832 sq in (53.7 sq dm)
Wing Loading:*24 - 26 oz/sq ft (73 - 79 g/sq dm)
Weight:*8.5 - 9.25lb (3850 - 4190g)
Airfoil:*Semi-symmetrical
Center of Gravity:*5.5" (139.7mm) Back from the leading edge of the
wing at the fuselage

Sig T- Clip 70
SPECIFICATIONS
Wing Span:70 in. (1778 mm)Wing Area:860 sq. in. (55.5 dm2)Length:50 in. (1270 mm)Flying
Weight:7 - 7.8 lbs. (3175 - 3538 g)Wing Loading:19 - 21 oz./sq. ft. (57 - 64 g/ dm2)Radio Req.4-Channel w/5 Standard Servos (glow)
4-Channel w/4 Standard Servos (electric)Glow Power:2-Stroke .53 - .61 cu. in. (8.6 - 10.0 cc)
4-Stroke .53 - .65 cu. in. (8.6 - 10.7 cc)Electric
Power:1200 - 1700 watt Brushless Motor
(300 - 400 kv)
75A Speed Control (ESC)
4S-6S 4000 - 5000 mAh Lipo Battery Pack

There's a thread on the Revolver powered with a 20cc gasser . Comparing specs I think the T Clip will make a good candidate for the 15-20cc gas engine.