Hi Jan,
Evidence gathered to date supports mufflers used on sandcast vins #1-7414 had no stamp marks.
To learn more about the exhaust differences, I'd suggest studying the info offered in our website.
Click on "Production Models," then click on #13 & #14, you will find some of the answers to your questions about exhaust differences.
Also, click on "Technical/Restoration Support," then click on #17, you can see pictures of the early and late exhaust features. You will also note more written differences between the different types of exhaust used on sandcast 750's.
Essentially there are two exhaust types used on the sandcast, neither stamped.
The major differences in these two exhaust occured at vin #'s 4148/4149.
Pre-4149 exhaust have 2.5 mm welded seams and a large baffle with no outside fiber packing. The early mufflers were essentially magaphone, no internal baffling.
Post-4148 mufflers have 5mm welded seams, a smaller baffle with outside fiber packing and internal baffling.
Early/late baffles will not interchange/fit with early/late mufflers.
Your vin, for correct aplication, uses early "Lotus Root" type mufflers.
Yamiya exhaust are a dead ringer for original, fit is perfect, overall finish better than original.
As far as i know, Yamiya supplies the late type exhaust only.
I am aware of no one who supplies an early type copy.
All heat shields, as used on the sandcast and diecast 69-70 750's are a satin finish. Yamiya sells these shields.
