Bill, your cylinder head for the 1098 is sitting still in the box you sent it in, you mention checking it out for a possible rebuild, I never even open the box, because I knew you're committed to the 1275 now, there no reason tho throw money at the 1098 head, rebuiding a head is not cheap. Long story short, call whenever you're ready to ship it back to you, and we can get it back with the engine. FWIW, if it is a 10CC 1098 engine, that means it has the bigger 2" mains, still while not in great demand, racers who use the 1098 engine for racing want the bigger main bearing engine.
As for retagging the engine with your old 1098 engine tag, you're not fool anyone who knows anything about these cars, the lack of lifter covers and and breather can on the timing cover of the 1275 are dead give-aways, anyway unless you are being judged in concourse judged show for originality, then who cares, all other shows are popular vote, and most people voting could care less if it is original, or probably would even know. Also IMHO, I would value a Sprite like your's at more value because it did have the 1275 engine. When I look at car like your's, I would value it more because it has all the stuff most people would want on a car like your Sprite, 1275, engine , alloy wheels, and such. These cars are just not valued that much for being absolute original, so people make them into what they want, and other people intrested in these a car would value these improvments as such as well.
For example, everytime I see some one who want to drive their car, say rebuild a 948, in sqaure body Spridget, I think, WHY throw good money at a 948, if you want to drive the car and enjoy it. Ok if you are into the originality thing, can't see I agree, but I get it. I just see these cars being built to enjoy, not like they will ever be of great value, like a Big Healey, Lotus, or a old Jag, so build them to enjoy!