Gawd, not another Victorian wanting to build a dark side cobra!.
Breeding like bluddy rabbits they are.
Now...here is my take on the whole deal. Harrison or G-Force.
Why?.....Harrison for fantastic service and a well shaped body and an excellent finished product.....G-Force for quality of body molding ( read cheaper to paint) and use of the Jag rear end.
RMC for excellent street manners ( a bit heavy for track), very strong chassis but poor body mold ( expensive to paint) and uses Jag rear end.
I have a soft spot for the Jag rear but I'm an elder statesman and a bit of a traditionalst.
Engine choice: Very hard to beat the Holden offerings for ease of fitment and cost/performance. Current 6Ltrs Gen4 offerings up to 300rwKw with cam, tune and cold air. Soon to be a 6.2 Ltr big brother of the L76 will offer much higher than 300rwKw. No problems getting the Gen4 accepted.
Just my opinion. I'm sure others will offer theirs.