You should be alright
HKS Regs here
http://www.japdragseries.co.uk/rules/General_Safety_Regulations_2010.doc
Important bits from it :
GSR 4:4 FRAMES
ALL CARS 9.99seconds and quicker, must have a serialised chassis sticker affixed to frame before participating in any event. Chassis certifications are available through MSA. Cars running 6.00 seconds or slower, chassis inspection every 36 months mandatory. Grinding of welds prohibited. All butt welds must have visible reinforcement (i.e. sleeve and rosette welds). Pressurisation of roll bar or roll cage in lieu of air bottles is prohibited. Visible reinforcement around any hole in any SFI spec chassis (not just the roll cage) mandatory. Reinforcement must be of at least the same cross sectional area as the hole, at least .049 inch (1.2 mm) thick chrome moly, and completely welded around the outside.
See 4:10 ROLL BARS and 4:11 ROLL CAGES.
GSR 4:10.1 MATERIAL & DIMENSIONS OF ROLL BAR.
Roll bar must be made of minimum O.D. of 45 mm (1 ¾ inches) x 3 mm (0.118 inch) mild steel,or minimum OD 45 mm (1 ¾ inches) x 2,1 mm (0.083 inch) chrome moly.
GSR 4:11 ROLL CAGE (ET 9.99 TO 8.50Secs)
Roll Cage: All cage structures must be designed in an attempt to protect the driver from any angle, 360-degrees and be fully welded. All 4130 chrome moly tube welding must be done by approved TIG heliarc process; mild steel tube welding must be approved MIG wire feed or TIG heliarc process. Welding must be free of slag and porosity. Any grinding of welds prohibited. Additionally, roll cage must be padded any where the driver’s helmet may contact it while in the driving position. In Competition eliminator where SFI Spec on chassis is required, padding must meet SFI Spec. 45.1