Don, this is a project I've considered too. I'm not a Husky guru, but FWIW here's what I planned as a suggestion, probably in this order:
1. Lose weight, lose weight, lose weight. Remove all the obvious things of course, incl excess brackets on frame. I'm lead to believe the frame is only slightly heavier than the CR (MJ/MK) frame so probably not worth replacing, but rear wheel & airbox are much heavier, so replace them w CR ones. Seatbase maybe worth replacing too. Alloy rims in place of steel ones. Lighter, smaller (alloy?) tank. Later (73/74ff) mag forks were lighter too, both sliders & tubes.
2. Power up. Start w better pipe & carb. RT was strangled w asthmatic pipe & small carb, but I suspect RT barrel maybe same as MX of the day (pre-reedvalve engine). If RT barrel is not sufficient try 74/75 reed-valve barrel. Or some porting. Maybe raise compression. All the usual stuff.
3. Suspension upgrade. YSS PD valve & decent shocks??
4. Gearbox ratios. RT ratios 1-4 are not too wide, but its a big jump to 5th (23%). If my specs are correct, replacing 5th gear w MX ratio closes the gap nicely to 16%. (5th gear MX is 0.74; 5th gear RT is 0.678; both are 0.88 for 4th as far as I can tell). Just rememeber it'll have to be from the 5sp MX box, not 6sp
5. VintageHusky type frame mod?? (for better steering - moves the seat forward & up, thereby improving the ergonomics & weight distribution) But this maybe technically illegal for pre-75 as it does change the position of the rear top shock mount a little.
