Actually, we Brits were operating a Lycoming Chipmunk back in the early 70s as a glider tug at Bicester. Very nice to fly, obviously better ptw ratio and much quieter cockpit. The electric start was handy too - we always hand swung our Gypsy chippies.
I don't think the Lycoming Chippies were as early as that. My late Father was in a syndicate with an ASW 15 (the ex-GSA glider, BGA1597, tail number: 29) and then a Kestrel 19 at Bicester until the beginning of 1975 when we moved to Duxford/Teversham. We were regular visitors to the GSA Centre after that and I
think the first time I saw a Lycoming Chippie there was late 1975, maybe early 1976. Albeit it was nearly 40 years ago so my memory could be shot!
While hand swinging went on I also remember the ex-UAS aircraft having cartridge starters.
We also had 2 ex-crop duster Gypsy chippies with fixed leading edge slots, both single seat. One had a squat little box canopy and was a real drag-master but nevertheless had good climb rate and superb slow speed handling. The other had a blown canopy and was a dream to fly. I'm sure the bubble produced extra lift as the climb performance seemed as good as the Lycoming aircraft - handled better too.
The teardrop canopied aircraft was G-ATVF which had been WD327 when in RAF service:
She certainly
wasn't a single seater, she had a front seat fitted. Although I grant you I can't remember her being a 2-sticker.
I spent many a time begging 'sandbag' trips in her in the early 1970's. To prove it, here is a shot of a very young (future) ExAscoteer clambering into the front seat. The year would have been 1973!
G-AOTF was one of the ag-chippys. Shown here in about 1985 with a 160 hp Lycoming in a fetching air defence grey colour scheme - which when you think about it has to be the worst colour to paint a tug. IIRC, she was a Mk23 which used a raised rear cockpit as the flying position, had a space for a hopper where the front seat was, and I think she had leading edge slots as well.
She certainly did have the leading edge slots although I can't find a photograph at the moment. When she had the Gypsy I remember her being a much lighter, almost silver, grey.